Delegate is a data structure that refers to a static method or to a class instance and an instance method of that class.
The closest equivalent of a delegate in Delphi Win32 is the method pointer.
Procedural Types and Procedure Pointers
Pas2JS lets you treat routines (functions and procedures) as values that can be assigned to variables.
Consider the nest code segment: 
Method Pointers
Similar to procedural pointers, method pointers reference a method of an instance object.
Here's one method pointer example:
Function pointers are unified, there is no distinction between standalone function and method pointers.
For instance the following code is valid as long as the function or method prototype matches.
type TMyFunction = function(n: Integer): string;
type myMethodDelegate = function(myInt: Integer): string of object; //----------------------------------------------------------------- TmySampleClass = class public function myStringMethod (myInt: Integer): string; class function mySignMethod (myInt: Integer): string; static; end;
{ mySampleClass }
class function TmySampleClass.mySignMethod (myInt: Integer): string; begin Result := ''; if (myInt > 0) then Result := '+'; if (myInt < 0) then Result := '-'; end;
function TmySampleClass.myStringMethod (myInt: Integer): string; begin Result := 'zero'; if (myInt > 0) then Result := 'positive'; if (myInt < 0) then Result := 'negative'; end;
procedure TForm1.W3Button7Click(Sender: TObject); var mySC: TmySampleClass; x: myMethodDelegate; y: myMethodDelegate; IntegerToString : TMyFunction;
begin IntegerToString := IntToStr; WriteLn(IntegerToString(12345));
mySC := TmySampleClass.Create; try WriteLn(Format('%d is %d; use the sign %d',[5, mySC.myStringMethod(5), mySC.mySignMethod(5)]) ); WriteLn(Format('%d is %d; use the sign %d',[-3, mySC.myStringMethod(-3), mySC.mySignMethod(-3)]) ); WriteLn(Format('%d is %d; use the sign %d',[0, mySC.myStringMethod(0), mySC.mySignMethod(0)]) ); WriteLn(sLineBreak);
{ Using Delegates } x := mySC.myStringMethod; y := mySC.mySignMethod; WriteLn(Format('%d is %d; use the sign %d',[5, x(5), y(5) ]) ); WriteLn(Format('%d is %d; use the sign %d',[-3, x(-3), y(-3)]) ); WriteLn(Format('%d is %d; use the sign %d',[0, x(0), y(0) ]) );
finally mySC.Free; end; end; |
As long as the function or method prototype matches.
You can use the @ operator to explicitly access a function reference to remove ambiguity.
Pas2JS nested routine example.
The function pointers and closures are unified, you don’t have to distinguish between a procedure and a procedure of object,
and you don’t have to distinguish a reference to procedure either.