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   ► KBTo/From GuidesDelphiData Structures  Print This     

Constructor (Cross Ref > Data Structures)

By Mike Prestwood

Delphi versus Access VBA: A side by side comparison between Delphi and Access VBA.

 
OOP Details
 

More object oriented (OO) stuff.

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?

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;
Access VBA:  "Constructors" Class_Initialize

When an object instance is created from a class, Access VBA calls a special parameter-less sub named Class_Initialize. Since you cannot specify parameters for this sub, you also cannot overload it.

When a class is destroyed, Access VBA calls a special sub called Class_Terminate.

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