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Parameters (Delphi and Delphi Prism Cross Reference Guide)

By Mike Prestwood

Delphi versus Delphi Prism: A side by side comparison between Delphi and Delphi Prism.

 
Language Details
 

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

Parameters

[Other Languages] 
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;
Delphi Prism:   var, const, out

Defining
Prism 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).

By Reference or Value (and by constant and out)
The default for parameters is by value. For by reference, add var in front of the parameter. Prism 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.) Finally, Prism offers an out parameter type which is like a var parameter except it does not have to be initialized prior.

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













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