how to do Generic like Implementation of class function in delphi

Question

i have a base class and 10 class derived from that class. Base class contain a function that except parameter of type procedure of object. like this

 mytype = procedure (a : integer) of object;

 baseclass = class
 public
   procedure myproc(cont handler : mytype ) ;
 end; 
 procedure baseclass.myproc(cont handler : mytype ) ;
 begin
 // do something
 end;

i am overloading this function in derived class i.e derived class contain same function but with different parameter (procedure ( const handler : integer ) of object ). like this

 base1mytype = procedure (a : string) of object; 

 derivedclass1 = class(baseclass)
 public
   procedure myproc(cont handler : base1mytype ) ;overload;
 end;

 base2mytype = procedure (a : boolean) of object; 
 derivedclass1 = class(baseclass)
 public
   procedure myproc(cont handler : base2mytype ) ;overload;
 end;

and so on.........

All i want a generic class that implement this function and i derive my classes from that function eg

   mytype = procedure (a : integer) of object;
    baseclass<T> = class
    public
      procedure myproc(cont handler : T) ;
    end; 
   procedure baseclass<T>.myproc(cont handler : T ) ;
   begin
   // do something
   end;
  and derive classes are like this

deriveclass1  = class<baseclass <string>>
  public
    procedure myproc(cont handler : T) ;
  end;

Since generic constraint does not support constrain of type procedure of object

I didn't read all of this yet, but I did notice that your code is not your real code. E.g. "cont" is not a valid keyword. Please post real code, not something you type into your web browser. That eradicates one big source of errors: typos. — Rudy Velthuis
I know that "const" was meant, but it shows you did not copy this from your editor, you typed it freehand into your browser. That often introduces typos which obfuscate the true and real problems. — Rudy Velthuis

David Heffernan David Heffernan · Accepted Answer · 2014-10-15T18:32:47

You need a generic class with an internal type definition:

type
  TBaseClass<T> = class
  public
    type
      THandler = procedure(Arg: T) of object;
  public
    procedure CallHandler(Handler: THandler; Arg: T);
  end;

procedure TBaseClass<T>.CallHandler(Handler: THandler; Arg: T);
begin
  Handler(Arg);
end;

how to do Generic like Implementation of class function in delphi

1 Answers