I.T. Discussion Community!
-Collapse +Expand
To/From Code
-Collapse +Expand Cross Ref Guide
-Collapse +Expand Members-Only
Sign in to see member-only pages.
   ► KBTo/From GuidesCorel Paradox  Print This     

Corel Paradox and Delphi Cross Reference Guide

By Mike Prestwood

Corel Paradox versus Delphi: A side by side comparison between Corel Paradox and Delphi.

Corel Paradox

Version: This content is based on Corel Paradox 11 (applies to the current version) but applies to earlier versions including Paradox 7, 8 , 9, and 10 as well (differences and exlusions are noted). The versions of Paradox sometimes known as 12, X3, X4, etc. are actually Paradox 11 with a patch (no real new features).

Delphi

CodeGear Delphi Helmet IconVersion: This content is based on Delphi 2009 and later and much of it verified in Delphi 2006.

To be clear, this content applies to Delphi for Win32. Delphi for .Net and Prism are documented under the Delphi Prism language topic. This content focuses on topics in common among the languages documented here so this content most likely applies to Delphi 2007 as well as earlier versions such as Delphi 5, 6, and 7.

 
Tool Basics
 

Developer environment basics such as common file extensions, common keyboard shortcuts, etc.

Deployment Overview

[Other Languages] 
Corel Paradox: 

To deploy a Paradox application, you need to deploy either the full version of Paradox or the Paradox Runtime both of which will include the BDE as well as any dependecies you've added such as psSendMail DLL, ezDialogs, etc.

More Info / Comment
Delphi: 

Delphi creates native code Windows applications so you can create an EXE with no dependencies that will run on any Windows computer. If you add dependencies (reports, database libraries, DLLs, etc.) use a Windows installer to build an installation program.

D2007 and D2009 are bundled with InstallAware Express CodeGear Edition installer.

More Info / Comment  




Development Tools

[Other Languages] 

Languages Focus

Primary development tool(s) used to develop and debug code.

Corel Paradox: 

Corel Paradox for Windows (was Borland Paradox). Also, Borland used to offer a Paradox for DOS tool which support it's Paradox Application Language (PAL) which is not compatible with ObjectPAL. The biggest drawback to Paradox is that Corel does not have anyone at Corel actively developing Paradox for Windows (as opposed to Microsoft Access which does).

Delphi: 

CodeGear Delphi is the primary tool of choice for most developers but other Object Pascal language development tools do exist and some are quite good.

More Info / Comment




File Extensions

[Other Languages] 

Languages Focus

Common or primary file extensions used (not a complete list, just the basics).

Corel Paradox: 

Paradox for Windows has two primary file types: source files and delivered files:

Source Files
Source files in Paradox are binary but can can be opened in later versions of Paradox and even in earlier versions if you don't use any new features.

  • .FSL = Form
  • .RSL = Report
  • .SSL = Script
  • .LSL = Library

Since Paradox source files do not compile to an EXE, Paradox developers tend to use a startup form or script to start the application.

Delphi: 

Common source code file extensions include:

  • .BDSPROJ - Project, Borland Developer Studio project file holds compiler options, etc. This is the file you open.
  • .DCU - Delphi Compiled Unit file.
  • .DFM - Delphi Win32 form file (a text resource file).
  • .DPR - Delphi project file. Primary project "source" file.
  • .PAS - Delphi unit source file.

Note: Delphi 2009 changed the project file to acommadatte new features. When you open a project file from a previous version, it will be upgraded. In addition to .bdsproj, D2009 also uses a .dproj project file.





Overview and History

[Other Languages] 
Corel Paradox: 

Language Overview: Object based language. Although ObjectPAL uses object oriented techniques "under the hood", it is not object oriented. Although you cannot create classes, ObjectPAL has built-in objects you can use in your code. You code in a traditional approach attaching code to objects or within a script. Most Paradox applications are form based. You may have a short startup script but you design forms and reports and tie them together with a common form. You can store reusable code such as custom methods and procedures in a library.

Target Platforms: Corel Paradox is most suitable for creating business desktop applications that run within Corel Paradox for Windows.

More Info / Comment  
Delphi: 

CodeGear Delphi Helmet IconLanguage Overview: Delphi programming language is a type-safe language consisting of hybrid traditional Pascal and OOP features. You code either in a traditional approach using functions, procedures, and global data, or you code using an OOP approach, or a mixture of both.

Target Platforms: Delphi for Win32 is most suitable for creating native code Win32 applications that run on Microsoft Windows.

More Info / Comment




Report Tools Overview

[Other Languages] 

Languages Focus

Built-In: Some development tools have a reporting tool built-in and some do not. For example, typically desktop databases such as Paradox and Access have a built-in reporting tool and typically that reporting tool is used with nearly every application built with it. A built-in reporting tool makes development of reports across many clients and applications consistent and therefore easy.

Add-On: Development tools that do not have a built-in reporting tool need to use either a currently bundled report writer, or one of the popular reporting tools that integrates well with the development tool. For example, popular reporting tools include Crystal Reports, ReportBuilder, and MS SQL Reporting Services (tied to MS SQL).

Corel Paradox:   Built-In

Paradox offers a built-in reporting tool that will suffice for most desktop database applications.

More Info / Comment
Delphi: 

Rave Reports comes closest to a Delphi standard now but historically there has been no real standard in Delphi development. Do-it-yourself developers sometimes like to use TPrinter for very simple reports. ReportSmith was bundled with the first few versions of Delphi.

Delphi has offered many embedded VCL component report options. Quick Reports has been a part of Delphi since Delphi 2.0 and has been the default report writer for many Delphi developers. Ace Reporter, ReportBuilder and Rave Reports are also very popular. During the time of Kylix, FastReports was popular because of it's cross-platform nature.

Crystal Reports is very common because of it's overall popularity as a stand-alone report writer that integrates well with many different tools.





 
Language Basics
 

Language basics is kind of a catch all for absolute beginner stuff. The items (common names) I chose for language basics is a bit random and include items like case sensitivity, commenting, declaring variables, etc.

Case Sensitivity

[Other Languages] 

Languages Focus

Case sensitiviy in this case is referring to commands and variable names. For example, are "printf" and "PrintF" equivalent? Are fullname and FullName equivalent? When you create commands, operations, methods, or variables should you worry about case?

Corel Paradox:   No

ObjectPAL is not case sensitive. My preference for ObjectPAL is to follow the camel casing promoted in the examples and help files originally developed by Borland.

Syntax Example:  

All of the following are equivalent:

msgInfo "", "Hello"
MsgInfo "", "Hello"
msginfo "", "Hello"
MSGINFO "", "Hello"

Variables are not case sensitive.

Var
FullName String
endVar
fullname="Mike Prestwood"
msgInfo("", fullNAME)
Delphi:   No

Object Pascal is generally not case sensitive.

Syntax Example:  

Variables and commands are not case sensitive.

var
FullName: String;
begin
fullname := 'Mike Prestwood';
ShowMessage(fullNAME);
SHOWMESSAGE(FULLNAME);
showmessage(fullname);
end;




Code Blocks

[Other Languages] 

Languages Focus

The rules for code blocks within a language dictate where you can declare variables, how you "bracket" code, etc.

Corel Paradox:   endXxxx

ObjectPAL code blocks are surrounded by statement ending keywords that all use End with camel caps such as endMethod, endVar, endIf, endSwitch, and endTry.

Syntax Example:
method
endMethod
 
var
endVar
 
if
endIf
 
switch
endSwitch
 
try
endTry
Delphi:   begin..end

Object Pascal requires the semi-colon after the "declaration" part.

Syntax Example:
function DoSomething : integer;
var
  a, b : integer
begin
  a := 1;
  b := 2;
  
  result := a + b;
end;




Comments

[Other Languages] 

Languages Focus

Commenting code generally has three purposes: to document your code, for psuedo coding prior to coding, and to embed compiler directives. Most languages support both a single line comment and a multiple line comment. Some languages also use comments to give instructions to the compiler or interpreter.

Corel Paradox:   ; and { ... }

Commenting Code
ObjectPAL uses ; for a single line comment and { } for a multiple line comment.

Syntax Example:  
;Single line comment.

{
Multiple line
comment.
}
Delphi:   // or { ... } or (* ... *)

Commenting Code
Delphi uses // for a single line comment and both {} and (**) for multiple line comments. Although you can nest different types of multiple line comments, it is recommended that you don't.

Compiler Directives - $
A special comment. Delphi compiler directives are in the form of {$DIRECTIVE}. Of interest for comments is using the $IFDEF compiler directive to remark out code.

Syntax Example:
//This is a single line comment.
 
{
Multiple line
comment.
}
 
(*
This too is a
multiple line comment.
*)
 
{$IFDEF TEMPOUT}
//...code here
{$ENDIF}




Constants

[Other Languages] 

General Info: Computer Language Constants

A constant is just like a variable (it holds a value) but, unlike a variable, you cannot change the value of a constant.

Corel Paradox:   const..endConst

In ObjectPAL, you declare one or more constant values within a const..endConst block. Optionally, you can specify the dataType by casting the value as part of the declaration.

If you do not specify the data type, the data type is inferred from the value as either a LongInt, a Number, a SmallInt, or a String.

As with variables, the const..endConst block can come within a method or procedure as the first bit of code, or in the Const window. Putting it above the method or procedure is allowed but has no significance so don't.

Syntax Example:
const
kFeetToMeter = Number(3.2808)
kMeterToFeet = Number(.3048)
kName = String("Mike")
  kCA = "California"     ;String inferred.
endConst
Delphi:   Const kPI: Double=3.1459;

In Delphi, you define constants similar to how you define variables but use the Const keyword instead of the Var keyword. Declare global constants in a unit's interface section and unit constants (scope limited to unit) in the implementation section. Declare local constants above the begin..end block.

Syntax Example:
Const 
  kFeetToMeter: Double = 3.2808;
  kMeterToFeet: Double = .3048;
  kName: String = "Mike";
 
//Local constants:
procedure SomeProcedure;
const
  kPI: Double=3.1459;
begin
end;




End of Statement

[Other Languages] 

Languages Focus

In coding languages, common End of statement specifiers include a semicolon and return (others exist too). Also of concern when studying a language is can you put two statements on a single code line and can you break a single statement into two or more code lines.

Corel Paradox:   whitespace

ObjectPAL is a bit unique in that it doesn't use a semicolon nor a return to mark the end of a line, it uses whitespace which can be a return, space, or tab. This is a bit unusual but does allow for some nice formatting of code.

Syntax Example:  
msgInfo("", "Hello1")
msgInfo("", "Hello2")
msgInfo("", "Hello3")

;The following single line of code also works.
msgInfo("", "Hello4") msgInfo("", "Hello5")

;Two or more works too:
msgInfo
("", "Hello6")
Delphi:   ;

Object Pascal uses a semicolon ";" as an end of statement specifier and you can put multiple statements on a single line of code and put a single statement on two or more code lines if you wish.

Syntax Example:  
WriteLn('Hello1');
WriteLn('Hello2');
WriteLn('Hello3');

//Same line works too:
WriteLn('Hello4'); WriteLn('Hello5');

//Two or more lines works too:
WriteLn
('Hello6');




Literals

[Other Languages] 

General Info: Programming Literals

A value directly written into the source code of a computer program (as opposed to an identifier like a variable or constant). Literals cannot be changed. Common types of literals include string literals, floating point literals, integer literals, and hexidemal literals. Literal strings are usually either quoted (") or use an apostrophe (') which is often referred to as a single quote. Sometimes quotes are inaccurately referred to as double quotes.

Languages Focus

In addition to understanding whether to use a quote or apostrophe for string literals, you also want to know how to specify and work with other types of literals including floating point literals. Some compilers allow leading and trailing decimals (.1 + .1), while some require a leading or trailing 0 as in (0.1 + 0.1). Also, because floating point literals are difficult for compilers to represent accurately, you need to understand how the compiler handles them and how to use rounding and trimming commands correctly for the nature of the project your are coding.

Corel Paradox:   quote

String literals are quoted as in "Prestwood". If you need to embed a quote use a slash in front of the quote as in \".

In ObjectPAL, string literals are limited to 255 characters but there's nothing preventing you from using multiple string literals together as in:

msgInfo("", "You can " + " add literals together in ObjectPAL") 

To specify a floating point literal between 1 and -1, you can preceed the decimal with a 0 or not (both work). In other words, preceding and following decimals are allowed (both .1 and 0.1). Trailing decimals are also allowed (1, 1., and 1.0 are all equivalent and allowed).

Syntax Example:  
msgInfo("", "Hello")
msgInfo("", "Hello \"Mike\".")
  
;Does ObjectPAL evaluate this simple
;floating point math correctly? No!
If (.1 + .1 + .1) = .3 Then
 msgInfo("", "Correct")
Else
 msgInfo("", "Not correct")
EndIf
Delphi:   apostrophe

String literals are single quoted (the apostrophe) as in 'Prestwood'. If you need to embed an apostrophe use two apostrophes in a row.

Floating point literals must start with an integer. For example, to specify a fractional floating point literal between 1 and -1, you preceed the decimal with a 0; otherwise, you will get a compiler error.

//x := .1 + .1;   //Does not work.
x := 0.1 + 0.1;   //Does work.
Syntax Example:  
ShowMessage('Hello');
ShowMessage('Hello Mike''s website.');




Variables

[Other Languages] 

Languages Focus

A variable holds a value that you can use and change throughout your code so long as the variable is within scope. With variable declaration, you not only want to know the syntax of how you declare a variable but you also want to know where. Are you allowed to declare a variable inline? What are the available scopes: local vs. global. Can you assign a value at the same time you declare a variable?

Corel Paradox:   var x SmallInt endVar

Declaring variables is optional unless you click Program | Compiler Warnings while in the ObjectPAL editor for every form, script, and library you create. Using Compiler Warnings is strongly recommended to avoid incorrectly typing an existing variable and to avoid any confusion about variable scope. Also recommended is turning on Compile with Debug for every form, script, and library too for tighter, cleaner code.

Undeclared variables are AnyType variables. Common data types include Currency, Date, Datetime, Logical, LongInt, Number, SmallInt, String, and Time.

Syntax Example:
var
    FullName String
    Age SmallInt
    Weight Number
endVar
 
FullName = "Mike Prestwood"
Age = 32
Weight =154.4
msgInfo("", FullName + ", age=" + String(Age) 
             + ", weight=" + String(Weight))
Delphi:   var x: Integer = 0;

The Delphi language is a strongly typed language so you have to specifically declare variables and frequently use commands such as IntToStr and StrToInt.

Declare global variables in the interface section of a unit, variables declared within the implementation section (but not within a method) have a scope limited to the unit. You declare local variables in a var block outside (above) your begin..end code block. You cannot declare variables in-line (inside begin..end).

You can initialize global and unit variables but you cannot initialize local variables.

Delphi offers many variable types. Some common variable types include String, WideString, PCharInteger, Boolean, Single, Double, Pointer, and Variant.

Note: D2009 introduced a new UnicodeString type.

Syntax Example:
procedure SomeProcedure;
var
  Fullname: String;
  Age: Integer;
  X, Y, Z: Double;
  MyArray: array [1..100] of Char;
begin
end;
 
//You can initialize global variables.
var
  ClickCounter: Integer = 0;




 
Language Details
 

Language Details is kind of a catch all for stuff that didn't make it into language basics nor any other category.

Custom Routines

[Other Languages] 

Languages Focus

For non-OOP languages, a custom routine is a function, procedure, or subroutine and for pure OOP languages, a custom routine is a class method. Hybrid languages (both non-OOP and OOP) combine both.

Corel Paradox:   method, procedure

ObjectPAL is a non-OOP language (an object-based language) that offers custom methods and custom procedures. When you create a custom method, you associate it with an existing object like a button, form, or library.

When calling a custom method or procedure that has a by reference parameter (uses var), then you cannot use a literal value. this is different than in many other languages which do allow you to pass literals by reference.

Syntax Example:
method sayHello(var pName String)
 msgInfo("", "Hello " + pName)
endMethod

method add(p1 Number, p2 Number) Number
 Return p1 + p2
endMethod
Delphi:   procedure, function

Delphi is a hybrid language so you can create either class methods (functions and procedures) or you can create global functions and procedures. When a function or procedure is part of a class, it is a class method.

[function/procedure] RoutineName : ReturnType;

As with C++, your custom routine must come before it's first usage or you have to prototype it in the Interface section.

Note: Contrast Delphi with Delphi Prism which is an OOP language (everything is within a class). Both Delphi and Delphi Prism are based on Object Pascal but implement OOP features differently and have some syntax differences too.

Syntax Example:
procedure SayHello(pName: String);
begin
  ShowMessage('Hello ' + pName);
end;
 
function Add(p1, p2 : Double): Double;
begin
  Result := p1 + p2;
end;




Event Handler

[Other Languages] 

In computer programming, an event handler is part of event driven programming where the events are created by the framework based on interpreting inputs. Each event allows you to add code to an application-level event generated by the underlying framework, typically GUI triggers such as a key press, mouse movement, action selection, and an expired timer. In addition, events can represent data changes, new data, etc. Specifically, an event handler is an asynchronous callback subroutine that handles inputs received in a program.

A custom event is a programmer created event. For example, you can contrast an event handler with a member event, an OOP concept where you add an event to a class.

Languages Focus

Many development environments and compilers provide for event driven programming, a standard set of application events such as startup, end, on click of a button, etc. This section documents the applicaton event handler or an overview for each language.

For OOP languages, do not confuse this section with class member events discussed in the OOP Details section of our Cross Reference Coding Encyclopedia.

[Not specified yet. Coming...]
Delphi: 

Many objects in Delphi have events you can use to trigger code. For example, when you add a form to your project you have access to the form events such as onCreate, onShow, onHide, onDockDrop, etc. In addition, Delphi offers module level events initialization and finalization sections.

More Info / Comment




Inline Code

[Other Languages] 

Languages Focus

Also known as embedded code where you embed another syntax language within the native code of the development environment you are using. The inline code can be compiled by the current development's compiler or by an external compiler.

Do not confuse with inlining which is a coding technique where custom routines are moved inline where the code is executed either by you, by a compiler directive, or automatically by the compiler.

Corel Paradox:   Not Supported
Delphi:   asm

In Delphi, you can inline assembler code using the asm keyword.

More Info / Comment




Inlining

[Other Languages] 

General Info: Inline Routines

Instead of calling a routine, you move the code from the routine itself and expand it in place of the call. In addition to manual inlining, some languages support automatic inlining where the compiler or some other pre-compiler decides when to inline a code routine. Also, some languages allow for developer defined inlining where the developer can suggest and/or force the inlining of a code routine. Inlining can optimize your code for speed by saving a call and return, and parameter management.

Languages Focus

Does it support inlining? If so, does it support developer defined inlining? Does it support automatic inlining? Both?

Corel Paradox:   Not Supported
Delphi:   Inline

Delphi introduced developer defined function and procedure inlining with Delphi 2005. Use the inline keyword to tell the compiler to try to inline a routine (a compiler hint). Since Delphi will only try to inline the routine, make sure you test for speed because inlining a routine can lead to slower code under some circumstances.

Syntax Example:  
function Add(a, b: Integer): Integer; inline;
begin
end;




Overloading

[Other Languages] 

Types of overloading include method overloading and operator overloading.

Method Overloading is where different functions with the same name are invoked based on the data types of the parameters passed or the number of parameters. Method overloading is a type of polymorphism and is also known as Parametric Polymorphism.

Operater Overloading allows an operator to behave differently based on the types of values used. For example, in some languages the + operator is used both to add numbers and to concatenate strings. Custom operator overloading is sometimes referred to as ad-hoc polymorphism.

Corel Paradox: 

Paradox & Overloading

  • Operator - No.
  • Method - No.

However, you can have the same named method or procedure so long as they are in different libraries. This is important if you use libraries in a class-like OOP way and wish to implement some form of polymorphism (i.e. libMember.Open and libVendor.Open). This is an OOP-like technique for implementing a subtyping-like polymorphism which is also known as inclusion polymorphism.

Also, some developers like to pass an array and then handle the array for a pseudo technique. Although not overloading, it's useful.

Delphi:   overload

Delphi supports both method and operator overloading.

For method overloading, you use the overload keyword (all versions of the routine must include the overload keyword). The compiler chooses the correct method first based on the number of parameters, then on the type so you can have two overloaded methods with the same number of parameters so long as at least one parameter is different.

Another form of method overloading is with the use of default parameters, a shortcut syntax, where you specify a default parameter value.

Delphi also supports operator overloading with some operators.

Syntax Example:
function Add(a, b: integer): Integer;  overload;
begin
Result := a+b;
end;
  
function Add(const msg: String; a, b: integer): String; overload;
begin
  Result := msg + IntToStr(a+b);
end;




Parameters

[Other Languages] 
Corel Paradox:   var, const

By Reference or Value (and by constant)
The default for parameters is by value. For by reference, add var in front of the parameter. ObjectPAL also offers constant parameters where you add const in front of the parameter. A constant parameter is like a read-only parameter the compiler can optimize. You cannot assign a value to a constant parameter.

Syntax Example:  
method cmCode(s String) ;...s is by value.
endMethod
 
  
method pushButton(var eventInfo Event)
  ;...eventInfo is by reference.
endMethod
  
method cmCode(Const s String)
  ;...s is a constant read-only parameter.
endMethod
  
proc cpNever() String
  return "Never duplicate a line of code!"
endProc

Delphi:   var, const

Object Pascal allows parameters of the same type to be listed together, separated by commas, and followed with a single data type (more params of different data types can follow, after a semi-colon).

Delphi also supports default parameters (a form of overloading).

By Reference or Value (and by constant): The default for parameters is by value. For by reference, add var in front of the parameter. Object Pascal also offers constant parameters where you add const in front of the parameter. A constant parameter is like a local constant or read-only parameter the compiler can optimize. You cannot assign a value to a constant parameter, nor can you pass one as a var parameter to another routine. (But when you pass an object reference as a constant parameter, you can still modify the object's properties.)

Syntax Example:
function Add(a, b: integer) : integer; 
begin
  Result := a + b;
end;
 
procedure ReplaceTime(var pDT: TDateTime; const pNewDT: TDateTime);
begin
end;




Self Keyword

[Other Languages] 
Corel Paradox:   Self

A built-in object variable that represents the UIObject to which the currently executing code is attached.

Syntax Example:  
method pushButton(var eventInfo Event)
  msgInfo("", self.Name)
endMethod
Delphi:   Self

Within the implementation of a method, the identifier Self references the object in which the method is called. The Self variable is an implicit parameter for each object method. A method can use this variable to refer to its owning class.

Syntax Example:
ShowMessage('Self=' + Self.ClassName);




 
Data Structures
 

Data structures allow you to store and work with data. Common data structures include arrays, associative arrays, etc.

Array

[Other Languages] 

Languages Focus

A data structure in which individual values (called elements or items) may be located by reference to one or more integer index variables, the number of such indices being the number of dimensions in the array.

Arrays can start with an index value of 0 or 1, sometimes referred to as 0 based or 1 based.

Corel Paradox:   Array[] type

Arrays in ObjectPAL use a 1-based subscript (also known as an index). Use [] with a subscript to refer to an element (i.e. MyArray[1], MyArray[2]).

The number of elements for a given array in ObjectPAL are either fixed or resizeable. Specify the size when you declare it for fixed. Use size() to get the number of elements, size() returns 0 if the array has no elements. Use setSize(), grow(), addLast(), etc. to add elements to an array.

Syntax Example:

var
  MyArray Array[4] String ;Fixed size array.
  i LongInt
endVar

MyArray[1] = "Mike"
MyArray[2] = "Lisa"
MyArray[3] = "Felicia"
MyArray[4] = "Nathan"

if MyArray.size() > 0 then
  for i from 1 to MyArray.size()
    msgInfo("", MyArray[i])
  endFor
endIf

Delphi:   x=Array[0..3] of string;

Delphi supports both static and dynamic arrays as well as single and multi dimensional arrays.

Syntax Example:
var
  MyArray: array[0..3] of string;
  i: Integer;
begin
  MyArray[0] := 'Mike';
  MyArray[1] := 'Lisa';
  MyArray[2] := 'Felicia';
  MyArray[3] := 'Nathan';
  
  for i := 0 to High(MyArray) do
    ShowMessage(MyArray[i]);
end;




Associative Array

[Other Languages] 
A set of unique keys linked to a set of values. Each unique key is associated with a value. Think of it as a two column table. MyArray['CA'] = 'California' MyArray['AR'] = 'Arizona'

Languages Focus

Associative arrays are also known as a dictionary or a hash table in other languages.

Corel Paradox:   DynArray

In ObjectPAL associative arrays are known as dynamic arrays.

Syntax Example:
var
myDynArray   DynArray[] String
endVar

 
myDynArray["Last_Name"] = "Spitz"
myDynArray["First_Name"] = "Randy"
myDynArray.view()
Delphi:   TStringList Assoc Array

Object Pascal doesn't have a native associative array, but you can use a TStringList the same way. (Alternatively, search the Internet for TStringHash and THashedStringList classes for implementations of a true associative array).

Syntax Example:
var
  StateList : TStringList;
begin
StateList := TStringList.Create; 
  StateList.CommaText := 'CA=California, FL=Florida';
  ShowMessage('FL is ' + StateList.Values['FL']);
end;




Pointers

[Other Languages] 

General Info: Pointers / References

A pointer is a variable type that allows you to refer indirectly to another object. Instead of holding data, a pointer holds the address to data -- the address of another variable or object. You can change the address value a pointer points to thus changing the variable or object the pointer is pointing to.

A reference is a type of pointer that cannot change and it must always point to a valid storage (no nulls).

Corel Paradox: 

ObjectPAL doesn't have a developer defined pointer type except for use with DLLs where you use a special CPTR uses keyword to refer to a DLL string pointer data type.

Syntax Example:  
Uses Tapi32
  tapiRequestMakeCall(sNumber CPTR, sAppName CPTR, 
    sLogName CPTR, sComment CPTR) CLONG
endUses
Delphi: 

Although pointer data types in Delphi coding are less important and not required for most general coding, Delphi fully supports developer defined pointers. Use a carrot (^) to declare a pointer data type. Use the @ operator or Addr function to return the current address of a variable.

Delphi provides typed pointer types such as PChar and PExtended as well as a generic point to anything Pointer type.

Nil is a special pointer value that you can assign to any type of pointer. Nil never points to any valid memory and indicates an unassigned or empty pointer.

Syntax Example:
//Declare a pointer of type integer.
PCounter : ^Integer;
  
//Assign a value to the location of a pointer.
//Also known as dereferencing.
PCounter^ := 8;
  
//Assign address of A to B.
PointerB := @PointerA;  //or...PointerB := Addr(PointerA);




 
Statements
 

Common statements such as if statements, loops, etc.

Exception Trapping

[Other Languages] 

Languages Focus

A common usage of exception handling is to obtain and use resources in a "try-it" block, deal with any exceptions in an "exceptions" block, and release the resources in some kind of "final" block which executes whether or not any exceptions are trapped.

Corel Paradox:   try...onFail

ObjectPAL has a try...onFail statement but does not have a finally-type component. However, the code afer endTry will execute.

try
onFail
endTry
Syntax Example:
var
i SmallInt
endVar
try
i = 0
i = 1/i
onFail
msgInfo("", "You cannot divide by zero.")
endTry
Delphi:   try..except, try..finally

Use a try..except..end block to trap and process errors.

Delphi also offers a try...finally where code will execute in the finally section no matter what. It's common to put a try..except inside a try..finally.

Syntax Example:
var
y : Double;
begin
try
y := 0;
y := (1/y);
ShowMessage(FloatToStr(y));
except
ShowMessage('You cannot divide by zero.');
end;
end;




If Statement

[Other Languages] 
Corel Paradox:   If..Else..EndIf, or switch

ObjectPAL supports a simple If...Else...EndIf statement.

Notice ObjectPAL does not support an ElseIf feature as part of an if statement. Instead use a switch statement

Syntax Example:  
'Does ObjectPAL evaluate the math correctly? No!
If (.1 + .1 + .1) = .3 Then
  msgInfo("", "Correct")
Else
  msgInfo("", "Not correct")
EndIf
 
'Switch statement example.
switch
case x = "Nate": MsgInfo("", "Hi Nate")
case x = "Felicia": MsgInfo("", "Hi Felly")
  otherwise: MsgInfo("", "Who are you?")
endSwitch
Delphi:   If..Else If..Else

Notice in the more complete example that the semicolon for the begin..end block after end is not included. That tells the compiler something else is coming (the statement is not finished). Also note the semicolon is missing right before the final "else" statement.

Note: The following example uses floating point literals. In Delphi, to specify a fractional floating point literal between 1 and -1, you preceed the decimal with a 0; otherwise, you will get a compiler error (i.e. .1 + .1 does not work).

Syntax Example:
if (0.1 + 0.1 + 0.1) = 0.3 then
  ShowMessage('Correct')
else
  ShowMessage('Not correct');
 
//Complete example:
if x = true then
begin
  ShowMessage('x is true');
end
Else If y = 'Mike' Then 
  ShowMessage('hello mike')
Else 
  ShowMessage('last option');




 
Operators
 

A language symbol used for assignment, comparison, computational, or as a logical.

Assignment

[Other Languages] 

Languages Focus

Common assignment operators for languages include =, ==, and :=. An assignment operator allows you to assign a value to a variable. The value can be a literal value like "Mike" or 42 or the value stored in another variable or returned by a function.

Corel Paradox:   =

ObjectPAL uses = for it's assignment operator.

Syntax Example:  
var
 FullName String
   Age SmallInt
endVar
  
FullName = "Randy Spitz"
Age = 42
Delphi:   :=

Delphi uses := for it's assignment operator.

Syntax Example:
var
  FullName: String;
  Age: Integer;
begin
  FullName := "Randy Spitz";
Age := 38;
end




Comparison Operators

[Other Languages] 

General Info: Round Floating Point Numbers

When comparing floating point numbers, make sure you round to an acceptable level of rounding for the type of application you are using.

Languages Focus

A comparison operator compares two values either literals as in "Hello" and 3 or variables as in X and Counter. Most languages use the same operators for comparing both numbers and strings. Perl, for example, uses separate sets of comparison operators for numbers and strings.

Corel Paradox:   =, <>

Common comparison operators:

= equal
<> not equal
< less than
> greater than
<= less than or equal
>= greater than or equal

Syntax Example:
'Does ObjectPAL evaluate the math correctly? No!
If .1 + .1 + .1 = .3 Then
msgInfo("", "correct")
Else
msgInfo("", "not correct")
endIf
Delphi:   =, <>

Common comparison operators:

= equal
<> not equal
< less than
> greater than
<= less than or equal
>= greater than or equal

Syntax Example:
//Does Delphi evaluate the math correctly? Yes!
//Refer to math.pas MaxSingle for more info.
if (0.1 + 0.1 + 0.1 = 0.3) then
ShowMessage('correct')
else
ShowMessage('not correct')




Empty String Check

[Other Languages] 

Languages Focus

An empty string is a zero length string, a string that is equal to null (""), or not assigned. In some languages, you can check if a string is empty by comparing it to an empty string (""). Some languages distinguish between nil and null ("") so checking if the length is 0 is easier.

Corel Paradox:   isBlank() or not isAssigned()

In ObjectPAL, an empty variable can be unassigned (essentially null) or blank (equivalent to ""). You have to use both isBlank and isAssigned to check for an empty string.

Syntax Example:
var
 s String
endVar
  
;s = ""  ;Uncomment to test 2nd case.
 
if isBlank(s) or not isAssigned(s) Then
 msgInfo("", "empty string")
endIf
Delphi:   length(s) = 0

Length() or SizeOf() will correctly identify an unassigned string variable or an empty string.

Syntax Example:
if length(s) = 0 then
  ShowMessage('empty string');




Logical Operators

[Other Languages] 

Languages Focus

Logical operators perform conditional and, or, and not operations. Some languages support both binary logical operators that link two and unary logical operators negate (make opposite) the truth value of its argument. Finally, some languages short circuit logic. For example, with this or that, if this is an expression returning true, then that is never executed.

Corel Paradox: 

ObjectPAL logical operators:

and and, as in this and that
or or, as in this or that
Not Not, as in Not This

Like VBA, ObjectPAL never short circuits. Given the expression this or that as well as this and that, if this evaluates to false, then that is still executed.

Syntax Example:
;Given expressions a, b, c, and d:
if Not (a and b) and (c or d) then
  ;Do something.
endIf
Delphi: 

Delphi logical operators:

and and, as in this and that
or or, as in this or that
not Not, as in Not This
xor either or, as in this or that but not both

The Delphi compiler default is to short circuit multi argument boolean expressions when the result is known before the evaluation completes. To disable short circuiting, use the {$B+} compiler directive. To reset it back to the compiler default of short circuting, use the {$B-} compiler directive.

Syntax Example:
//Given expressions a, b, c, and d:
if Not (a and b) and (c or d) then
  //Do something.




String Concatenation

[Other Languages] 
Corel Paradox:  "String Concatenation" +

String literals s are limited to 255 characters but you can simply add two strings together as in:

s = "A long string." + "Another long string."
Syntax Example:
var
FirstName  String
  LastName  String
endVar
 
FirstName  = "Mike"
LastName  = "Prestwood"
msgInfo("", "Full name: " + FirstName + " " + LastName)
Delphi:  "String Concatenation" +

Use the + operator to concatenate two strings. Use IntToStr to convert an integer to a string and FloatToStr to convert a floating point number to a string.

Syntax Example:
var 
  FirstName : String; 
  LastName : String;
begin 
  FirstName := 'Mike'; 
  LastName := 'Prestwood';
  ShowMessage('Full name: ' + FirstName + ' ' + LastName);
  
  ShowMessage(FloatToStr(3.2));
end;




Unary Operators

[Other Languages] 

General Info: Unary Operator

An operation with only one operand (a single input). Common unary operators include + plus, - minus, and bitwise not. Some operators can function as both unary and binary operators. For example, + and - operators can serve as either.

Languages Focus

What unary operators are supported in additoin to the standard plus, minus, and bitwise not.

Corel Paradox: 

The ObjectPAL unary operators are:

+
-
Not

More Info / Comment
Delphi: 

An operation with only one operand (a single input). In Object Pascal, a unary operator has the highest precedence and always precedes its operand (for example, -B), except for the  ^ pointer operator, which follows its operand (for example, P^). In addition to the obvious +, -, and Not operators, Delphi also offers:

^ Pointer
@ returns the address of a variable, function, procedure, or method; a pointer to its operand.
inc() Increment
dec() Decrement

The TYPE operator is also a unary operator and is valuated at compile time. The TYPE operator returns the size in bytes of the operand,

More Info / Comment




 
Commands
 

Common commands (procedures and functions). A function returns a value. Optionally, it may also perform an action prior to returning a value. A procedure does not return a value or it returns void or null.

Left of String

[Other Languages] 
Corel Paradox:   subStr

substr ( const startIndex LongInt [ , const numberOfChars LongInt ] ) String

Alternative syntax:

LeftString = subStr(NameVar, 1, 3)
Syntax Example:
var
�LeftString String;
  NameVar String;
endVar
NameVar = "Prestwood"
LeftString = NameVar.subStr(1, 3)
msgInfo("", LeftString)
Delphi:   LeftStr
Syntax Example:
Uses StrUtils;
ShowMessage(LeftStr('Prestwood', 3));




 
Database
 

This category documents connecting and using data including database commands, and common technologies used.

Edit Record

[Other Languages] 

Languages Focus

This common syntax name documents editing a record as a whole: add/insert, edit, post data, and delete.

Corel Paradox:   insertRecord, postRecord, edit

In ObjectPAL, you use Cursor.InsertRecord to add a new record, Cursor.postRecord to post the record, and Cursor.deleteRecord() to delete it. To edit a record, you must put the cursor into edit mode, Cursor.Edit(). (A cursor applies to both a TCursor and UIObject.)

ObjectPAL gives you tremendous flexibility with editing data and includes many additional commands such as insertAfterRecord and isEdit. For dBASE tables, you can also use unDeleteRecord() to un-delete a record. See the ObjectPAL help for more commands.

Syntax Example:

The following code snippet adds a record to a given TCursor with FullName and Created fields:

tc.edit()
tc.InsertRecord()
tc.FullName = "Barack Obama"
tc.Created  = today()
tc.postRecord
[Not specified yet. Coming...]




Filter Records

[Other Languages] 
Corel Paradox:   setRanger, setGenFilter

In ObjectPAL, you can filter set a TCursor, UIObject, and Table objects using setRange() and setGenFilter().

Syntax Example:

The following example loads, filters, and runs a report.

var
 r Report
 dyn DynArray[] String
endVar
  
dyn["Name"] = "SCUBA Heaven"
Customer.setGenFilter(dyn)
  
r.load(":Sample:customer")
r.Customer.setGenFilter(dyn)
r.run()

You can also drop a flter with:

r.Customer.dropGenFilter()
[Not specified yet. Coming...]




Find Record

[Other Languages] 

Languages Focus

Finding a record is about moving a cursor to a specific record within a set of records (documented here). In addition to finding a record, you can sort, filter, and loop a set of records (documented in their topics).

Corel Paradox:   locate, qLocate

ObjectPAL provides a rich set of commands for finding a record with a TCursor or UIObject including:

  • locate() -  Seach for a value based on a criteria. Uses indexes as appropriate.
  • locatePattern() - Search for a pattern within a value.
  • moveToRecord() - Moves to a specific record number.
  • qLocate() - Search using currently set index.

Each of these basic find record commands has supporting commands such as locateNext() and recNo().

Syntax Example:
var
  tc TCursor
endVar
   
tc.open("Customer.db") 
if tc.locate("Name", "Proffessional Divers, Ltd.") then 
  tc.edit()
  tc.Name = "Professional Divers, Ltd."
  msgInfo("Success", "Corrected spelling error.")
endIf
tc.endEdit()
[Not specified yet. Coming...]




Record Movement

[Other Languages] 

Languages Focus

Top, bottom, next, and previous.

Corel Paradox:   home, end, nextRecord

ObjectPAL uses home(), end(), nextRecord(), priorRecord() to move a database cursor (works with either a TCursor or UIObject).

TCursor.nextRecord()

These commands send a message to the object. Specifically, they send an action constant using the action command. The above snippet is equivalent to:

TCursor.action(DataNextRecord)

It is handy to  with familiar with action constants because not all action constants have an ObjectPAL equivalent comment.

Syntax Example:

The following snippet uses the active keyword to move to the second to last record of the table attached to the UIObject that currently has focus:

active.end()
active.priorRecord()

You can also use the self keyword to refer to the UIObject your code is attached to.

[Not specified yet. Coming...]




Sort Records

[Other Languages] 
Corel Paradox:   switchIndex, sortTo, setGenFilter

In Paradox, you add an index for each sort your wish to perform on a table then use switchIndex(). Alternatively, you can use sortTo() to sort a table into a new table.

More Info / Comment
[Not specified yet. Coming...]




 
OOP Basics
 

Some languages support object-based concepts such as Paradox, Access, and VB Classic. Other languages have OO extensions and fully support object orientation in a hybrid fashion (such as C++ and Dephi for Win32). Finally, some lanages such as C#, VB.Net, Prism, and Java are entirely written in OO. Meaning, every line of code written must occur within a class).

Base Class

[Other Languages] 

Languages Focus

When you create a class, it is either a base class or inherits from another class. Some languages require all classes to inherit from a common base class and some do not.

Corel Paradox:   Not Supported
Delphi:   TObject

In Delphi programming language (Object Pascal), all classes ultimately inherit from the base class TObject.

Syntax Example:
//Specify both namespace and class:
TCyborg = class(System.TObject)
end;
  
//Use shortcut alias:
TCyborg = class(TObject)
end;
  
//None, default is System.TObject
TCyborg = class
end;




Class..Object

[Other Languages] 

Languages Focus

In short, a class is a data type, and an object is an instance of a class type. A class has methods (routines), properties (member variables), and a constructor. The current values of the properties is the current state of the object. The UML is one of the diagraming disciplines that allows you to document the various changing states of a series of objects.

Corel Paradox:   Not Supported
Delphi:   class..end..Create

Declare your class in the Interface section. Then implement the class in the Implementation section. To create an object instance, call the class constructor (usually named Create). Since Delphi does not have a garbage collector, you have to also free the object usually with either Free or FreeAndNil.

Syntax Example:
//Interface section:
TCyborg = class(TObject)
public
procedure IntroduceYourself;
end;
 
//Implementation section;
procedure TCyborg.IntroduceYourself;
begin
ShowMessage('Hi, I do not have a name yet.');
end;
 
//Some event like a button click:
var
T1: TCyborg;
begin
T1 := T1.Create;
T1.IntroduceYourself;
  FreeAndNil(T1);      //Be sure to clean up!
end;




Inheritance

[Other Languages] 

The concept of a class makes it possible to define subclasses that share some or all of the main class characteristics. This is called inheritance. Inheritance also allows you to reuse code more efficiently. In a class tree, inheritance is used to design classes vertically. (You can use Interfaces to design classes horizontally within a class tree.) With inheritance, you are defining an "is-a" relationship (i.e. a chow is-a dog). Analysts using UML call this generalization where you generalize specific classes into general parent classes.

Corel Paradox:   Not Supported

ObjectPAL does not support class creation nor sub-classing (inheritance).

Delphi:   =class(ParentClass)

In Delphi, you use the class keyword followed by the parent class in parens. If you leave out the parent class, your class inherits from TObject.

Syntax Example:

In the following example, a terminator T-600 is-an android. 

TAndroid = class
end;
 
T-600 = class(TAndroid)
end;




Member Event

[Other Languages] 

A custom event added by a programmer to a class. Custom created events need to be processed, usually by an event dispatcher within a framework.

[Not specified yet. Coming...]
Delphi:  "Member Events"

In Delphi, member events are essentially properties of the type method pointer.

More Info / Comment




Member Field

[Other Languages] 

Also known as a Class Field.

A class variable defined with a specific class visibility, usually private visibility. A member property is different than a member field. A member property uses a member field to store values through accessor methods (getters and setters). For example, it is common to use a private member field to store the current value of a property. The current values of all the class member fields is the current state of the object.

Languages Focus

What modifiers apply to member fields, if any? Typical member field modifiers include scope modifiers (private, protected, etc.) and read-only. Can you initialize the value of a member field when declared ensuring a default value?

Corel Paradox:   Not Supported
Delphi: 

In Delphi, it is common to start all member fields with "F" as in FName and FAge. You can initialize the value of member fields too.

Delphi member fields do not support static data. The workaround is to use the hybrid nature of Delphi and use a unit variable (a variable declared in the implementation section of a unit) and then access the unit variable with a member property.

Delphi doesn't support setting a member field to read-only. However, you can accomplish the task with a strict private member field and a read-only property.

Syntax Example:
TCyborg = class(TObject)
private
  FSerialNumber: String='A100';
public
FCyborgName: String;
FCyborgAge: Integer=0;

  FSeriesID: Integer=100;
end;




Member Method

[Other Languages] 

Also known as a Class Method.

A code routine that belongs to the class or an object instance (an instance of the class). Methods that belong to the class are called class methods or static methods. Methods that belong to an object instance are called instance methods, or simply methods.

When a method returns a value, it is a function method. When no value is returned (or void), it is a procedure method.

Methods frequently use method parameters to transfer data. When one object instance calls another object instance using a method with parameters, you call that messaging.

Corel Paradox:   Not Supported
Delphi:   procedure, function

Delphi uses the keywords procedure and function. A procedure does not return a value and a function does.

Syntax Example:
//Interface section:
TCyborg = class(TObject)
public
  procedure IntroduceYourself;
end;
 
//Implementation section;
procedure TCyborg.IntroduceYourself;
begin
  ShowMessage('Hi, I do not have a name yet.');
end;
 
//Some event like a button click:
var
  T1: TCyborg;
begin
  T1 := T1.Create;
  T1.IntroduceYourself;
end;




Member Modifier

[Other Languages] 

Languages Focus

Traditional private, protected, public, etc. member modifiers are documented under the member visibility topic of the Cross Reference Encyclopedia. With member modifiers here, we address additional member modifiers such as method and field modifiers.

Corel Paradox:  "Member Modifiers" Not Supported
Delphi:  "Member Modifiers"

Specify Delphi member modifiers as follows:

reintroduce; overload; [binding modifier]; [calling convention]; abstract; [warning]

The binding modifiers are virtual, dynamic, or override.

The calling conventions are register, pascal, cdecl, stdcall, or safecall.

The warnings are platform, deprecated, or library.

Additional directives include reintroduce, abstract, class, static, overload, and message.

Syntax Example:
TCyborg = class(TObject)
public
  procedure Speak(pMessage: String); virtual;
end;
 
TSeries888 = class(TCyborg)
public
  procedure Speak(pMessage: String); override;
end;




Member Property

[Other Languages] 
Corel Paradox:   Not Supported
Delphi:   property..read..write

Delphi uses a special property keyword to both get and set the values of properties. The read and write keywords are used to get and set the value of the property directly or through an accessor method. For a read-only property, leave out the write portion of the declaration.

You can give properties any visibility you wish (private, protected, etc). It is common in Delphi to start member fields with "F" ("FName" in our example) and drop the "F" with properties that manage member fields ("Name" in our example).

Syntax Example:
TCyborg = class(TObject)
private
  FCName: String;
public
  property CyborgName: String read FCName write FCName;
end;




Member Visibility

[Other Languages] 

General Info: Class Visibility Specifiers

In OOP languages, members of a class have a specific scope that indicates visibility. Standard visibility includes private, protected, and public. Private members are usable by the defining class only (fully encapsulated). They are invisible outside of the class except by friendly classes. Protected members are usable by the defining class and descendant classes only (plus friendly classes). Public members are usable wherever its class can be referenced.

Languages Focus

Traditional member visibility specifiers for fully OOP languages are private, protected, and public. Many modern OOP languages implement additional member visibilities.

Additional member modifiers are documented under the Member Modifiers topic.

Corel Paradox:   Not Supported
Delphi: 

In Delphi, you group member declarations as part of defining the interface for a class in the Interface section of a unit.

Up until D2005, private and protected were not implemented strictly. Starting with D2005, a traditional strict versions of OOP are supported using the strict keyword. OO purist will want you to use strict private over private and strict protected over protected. I suggest you follow that advice until you both fully understand the differences and have a specific need.

Delphi offers a special published specifier which is the same as public members but runtime type information (RTTI) is generated.

Syntax Example:
TCyborg = class(System.Object)
private
//Don't use accept when you really want private friendly members.
strict private
//Use as your default private members.
  FName: String;
protected
//Don't use accept when you really want protected friendly members.
strict protected
//Use as your default protected members.
public
  

published
  //RTTI Info

end;




 
OOP Details
 

More object oriented (OO) stuff.

Abstraction

[Other Languages] 

General Info: Abstract Class / Abstract Member

An abstract class member is a member that is specified in a class but not implemented. Classes that inherit from the class will have to implement the abstract member. Abstract members are a technique for ensuring a common interface with descendant classes. An abstract class is a class you cannot instantiate. A pure abstract class is a class with only abstract members.

Languages Focus

Abstraction is supported at various levels with each language. A language could enforce abstraction at the class level (either enforcing a no-instantiation rule or a only abstract members rule), and with class members (member methods and/or properties).

Corel Paradox:   Not Supported
Delphi:   abstract, override

Delphi for Win32 supports abstract class members using the abstract keyword. You can even instantiate instances of a class that contains abstract members. Then you override each abstract member in a descendant class with Override.

Delphi does not support setting an entire class as abstract. You can create an abstract class (a class with one or more abstract methods), but there is no way to tell the compiler to not allow the instantiation of the abstract class.

Delphi does not support abstract member properties directly. To implement an abstract properity, make use of abstract methods. That is, you can read a GetPropertyX abstract function and write to a SetPropertyX abstract procedure. In effect, creating  an abstract property.

Syntax Example:
TCyborg = class(TObject)
public
  procedure Speak(pMessage: String); virtual; abstract;
  procedure Walk; virtual; abstract;
end;
 
TSeries600 = class(TCyborg)
public
  procedure Speak(pMessage: String); override;
  procedure Walk; override;
end;




Class Helper

[Other Languages] 

A. In Dephi, class helpers allow you to extend a class without using inheritance. With a class helper, you do not have to create and use a new class descending from a class but instead you enhance the class directly and continue using it as you always have (even just with the DCU).

B. In general terms, developers sometimes use the term to refer to any class that helps out another class.

Corel Paradox:  "Class Helpers" Not Supported
Delphi:  "Class Helpers" class helper for

Delphi allows you to extend an existing class without using inheritance. Buggy in 2005 and not officially supported but stable, usable, and officially supported in 2006 and above.

You declare a class helper similiar to how you declare a class but use the keywords class helper for.

Syntax Example:
TCyborg = class(TObject)
public
  FCyborgName: String;
end;
  
TCyborgHelper = class helper for TCyborg
  procedure ShowClassName;
end;




Code Contract

[Other Languages] 

A.k.a. Class Contract and Design by Contracts.

A contract with a method that must be true upon calling (pre) or exiting (post). A pre-condition contract must be true when the method is called. A post-condition contract must be true when exiting. If either are not true, an error is raised. For example, you can use code contracts to check for the validity of input parameters, and results

An invariant is also a code contract which validates the state of the object required by the method.

Corel Paradox:  "Code Contracts" Not Supported
Delphi:  "Code Contracts" Not Supported

Delphi does not offer built-in Design by Contract features. It does offer an Assert method which tests if an expression is true. If false, an EAssertionFailed exception is raised. Although you can use Assert in a similar manor as you would use a pre-condition contract, the Delphi help clearly says Assert is a debugging tool only and to not use it in production code.

//Although not intended as a code contract feature,
//Assert is useful for debugging.
method Cyborg.Walk(pPace);
begin
Assert(pPace > 0);
Assert(pPace < 100);
  
  //Overloaded version with message.
Assert(FEnergyLevel >= 10, 'Energy level too low.');
end;




Constructor

[Other Languages] 

General Info: Class Constructor

Constructors are called when you instantiate an object from a class. This is where you can initialize variables and put code you wish executed each time the class is created. When you initially set the member fields and properties of an object, you are initializing the state of the object. The state of an object is the values of all it's member fields and properties at a given time.

Languages Focus

What is the syntax? Can you overload constructors? Is a special method name reserved for constructors?

Corel Paradox:  "Constructors" Not Supported
Delphi:  "Constructors" constructor

In Delphi, use the constructor keyword to signify which method or methods are constructors for a class. It is traditional but not required to use a procedure called Create.

In addition to having multiple named constructors, you can overload constructors.

Syntax Example:
//Interface section.
TCyborg = class(TObject)
public
  constructor Create;
end; 

Then implement the class constructor in the Implementation section.

constructor TCyborg.Create;
begin
  inherited;  //Call the parent Create method
end;




Destructor

[Other Languages] 

General Info: Class Destructor

A special class method called when an object instance of a class is destroyed. With some languages they are called when the object instance goes out of scope, with some languages you specifically have to call the destructor in code to destroy the object, and others use a garbage collector to dispose of object instances at specific times.

Desctructors are commonly used to free the object instance but with languages that have a garbage collector object instances are disposed of when appropriate. Either way, destructors or their equivalent are commonly used to free up resources allocated in the class constructor.

Languages Focus

Are object instances freed with a garbage collector? Or, do you have to destroy object instances.

Corel Paradox:   Not Supported
Delphi:   Free or FreeAndNil

Object Pascal uses a standard virtual destructor named Destroy which is called by the standard Free method. All objects are dynamic, so you need to call MyObject.Free method or the FreeAndNil(MyObject) routine for each object you create.

Syntax Example:  
var
MyObject: TObject;
begin
MyObject := TObject.Create;
 
  //Use it...
  
  MyObject.Free
  //Or use...FreeAndNil(MyObject);
end;




Inheritance-Multiple

[Other Languages] 
Corel Paradox:   Not Supported
Delphi:   Not Supported

Delphi does not support multiple implementation inheritance. Each class can have only one parent class (a single inheritance path).

In Delphi, you can use multiple interface usage to design in a multiple class way horizontally in a class hierarchy.

More Info / Comment




Interface

[Other Languages] 

An element of coding where you define a common set of properties and methods for use with the design of two or more classes.

Both interfaces and abstract classes are types of abstraction. With interfaces, like abstract classes, you cannot provide any implementation. However, unlike abstract classes, interfaces are not based on inheritance. You can apply an Interface to any class in your class tree. In a real sense, interfaces are a technique for designing horizontally in a class hierarchy (as opposed to inheritance where you design vertically). Using interfaces in your class design allows your system to evolve without breaking existing code.

Corel Paradox:  "Interfaces" Not Supported
Delphi:  "Interfaces" IInterface, TInterfacedObject

In Delphi, you use interfaces for both com objects and language interfaces and make use of IUnknown, IInterface, and/or TInterfacedObject.

For a pure language interface, add your specified proprieties, procedures, and functions to an interface that descends from IInterface (the base interface) as an interface, no implementation. Then have your implementing class inherit from TInterfacedObject and implement the interface.

For extending the VCL, you descend from the class you wish to extend, then implement an interface from IInterface and add the required functions QueryInterface, _AddRef, and _Release methods (refer to TInterfacedObject for an example).

For a com object, you descend from IUnknown. Descending from IUnknown instead of IInterface informs the Delphi compiler that the interface must be compatible with COM objects -- a Windows feature).

When defining an interface, define it in the type block just like you do for a class but you use the interface keyword instead of the class keyword and in the interfaces section only. Since interfaces, by definition, do not have any implementation details, all you do is specify it in the type block. Then implement in all classes that support the interface.

Syntax Example:
//Language interface:
//Interface section of unit.
IHuman = Interface(IInterface)
  //Specify interface methods and properties here.

end;
  
TCyborg = class(TInterfacedObject)
end;
  
TCyborgHuman = class(TCyborg, IHuman)
//Specify each here and implement in
//implementation section.
end;




Overriding

[Other Languages] 

General Info: Method Overriding

Where you define or implement a virtual method in a parent class and then replace it in a descendant class.

When you decide to declare a method as virtual, you are giving permission to derived classes to extend and override the method with their own implementation. You can have the extended method call the parent method's code too.

In most OO languages you can also choose to hide a parent method. When you introduce a new implementation of the same named method with the same signature without overriding, you are hiding the parent method.

Corel Paradox:   Not Supported
Delphi:   virtual, override

In Delphi, you specify a virtual method with the virtual keyword in a parent class and extend (or replace) it in a descendant class using the override keyword. Call Inherited in the descendant method to execute the code in the parent method.

Syntax Example:
TRobot = class(TObject)
public
procedure Speak; virtual;
end;
  
TCyborg = class(TRobot)
procedure Speak; Override;
end;




Partial Class

[Other Languages] 

A partial class, or partial type, is a class that can be split into two or more source code files and/or two or more locations within the same source file. Each partial class is known as a class part or just a part. Logically, partial classes do not make any difference to the compiler. The compiler puts the class together at compile time and treats the final class or type as a single entity exactly the same as if all the source code was in a single location.

Languages Focus

For languages that have implemented partial classes, you need to know usage details and restrictions. Can you split a class into two or more files? Can you split a class within a source code file into two or more locations? What are the details of inheritance? Does it apply to interfaces as well?

Corel Paradox:  "Partial Classes" Not Supported
Delphi:  "Partial Classes" Not Supported

As of Delphi 2009, partial classes are not supported. The main reason given in the thread below was that the Delphi compiler is a single pass compiler. Here is a link to a discussion thread on the subject:





Polymorphism

[Other Languages] 

A coding technique where the same named function, operator, or object behaves differently depending on outside input or influences. Usually implemented as parameter overloading where the same named function is overloaded with other versions that are called either with a different type or number of parameters. Polymorphism is a general coding technique and other specific implementations are common such as inheritance, operator overloading, and interfaces.

Languages Focus

Many languages support built-in polymorphism such as a "+" operator that can add both integers and decimals. The following documents the ability to implement developer defined polymorphism.

Corel Paradox:   Not Supported

Built-in: In ObjectPAL, polymorphism is the capability of the built-in objects to act differently depending on the context in which they are being used. For example, Table.Open and TCursor.Open. The Open method works differently depending on the object type used.

Custom: No. However, you can have the same named method or procedure so long as they are in different libraries. This is important if you use libraries in a class-like OOP way and wish to implement some form of interfaces-like polymorphism (i.e. libMember.GetName and libVendor.GetName).

More Info / Comment
Delphi: 

Delphi supports the following types of polymorphism:

More Info / Comment




Prevent Derivation

[Other Languages] 

Languages Focus

How do you prevent another class from inheriting and/or prevent a class from overriding a member.

Corel Paradox:   Not Supported
Delphi:  "Sealed class" sealed, final

With Delphi, use the sealed keyword to prevent a class from being inherited from and use the final keyword to prevent a method from being overridden.

Syntax Example:
type
  Robot = class sealed(TObject)
public
  procedure Speak(pSentence: String); virtual; final;
end;




Static Member

[Other Languages] 

General Info: Static Class / Static Member

A static member is a member you can have access to without instantiating the class into an object. For example, you can read and write static properties and call static methods without ever creating the class. Static members are also called class members (class methods, class properties, etc.) since they belong to the class and not to a specific object. A static class is a class that contains only static members. In the UML, these classes are described as utility classes.

Languages Focus

Languages that support static members usually at least support static member fields (the data). Some languages also support static methods, properties, etc. in which case the class member is held in memory at one location and shared with all objects. Finally, some languages support static classes which usually means the compiler will make sure a static class contains only static members.

Corel Paradox:  "Static Members" Not Supported
Delphi:  "Class Members" Class

Object Pascal supports static methods, but not static member fields. For static member fields, use traditional Pascal-like global variables.

Since Object Pascal is a hybrid language, you can use global functions and data so the need for class methods is diminished but still useful. For example, since Object Pascal does not have automatic reference counting, you could use a class method to keep track of the number of object instances.

Delphi 1-7: All classes in a unit are friendly (see eachother's private members), some developers like to put each class in it's own unit and reserve putting multiple classes in the same unit until they wish to implement friendly classes.

Delphi 2005+: New strict keyword allows you to indicate friendly.

Delphi Prism: The Strict keyword was introduced from the beginning (Delphi.Net preview that shipped with D7).

Syntax Example:
type
TMyUtils = class(TObject)
public
class function MyStaticMethod: Integer;
end;

In implimentation:

class function TMyUtils.MyStaticMethod: Integer;





Follow PrestwoodBoards on: 


©1995-2019 PrestwoodBoards  [Security & Privacy]
Professional IT Services: Coding | Websites | Computer Tech