Hello,

How to use this code below in mode objfpc?:

  TMyGeneric<T> = class(TObject)
  private
    FValue: T;
  public
    property Value: T read FValue write FValue;
  end;

...

var
  VMyGenericStr: TMyGeneric<Integer>;
  VMyGenericInt: TMyGeneric<string>;
begin
  VMyGenericStr := TMyGeneric<Integer>.Create;
  VMyGenericStr.Value := 2014;
  VMyGenericStr.Free;
  VMyGenericInt := TMyGeneric<string>.Create;
  VMyGenericInt.Value := 'Delphi Generics';
  VMyGenericInt.Free;
end;

When I try:

  generic TMyGeneric<T> = class(TObject)
  private
    FValue: T;
  public
    property Value: T read FValue write FValue;
  end;

...

var
  VMyGenericStr: specialize TMyGeneric<Integer>;
  VMyGenericInt: specialize TMyGeneric<string>;
begin
  VMyGenericStr := TMyGeneric<Integer>.Create;
  VMyGenericStr.Value := 2014;
  VMyGenericStr.Free;
  VMyGenericInt := TMyGeneric<string>.Create;
  VMyGenericInt.Value := 'Delphi Generics';
  VMyGenericInt.Free;
end;

I got:

Error: Illegal expression
Error: Operator is not overloaded: "Class Of TMyGeneric$1" < "LongInt" Fatal: Syntax error, ";" expected but "identifier CREATE" found

Thank you!

ps: FPC from trunk.

AFAIK, you must create a new type:

type
    TMyGenericInt = specialize TMyGeneric<Integer>;
var
    VMyGenericInt: TMyGenericInt;
begin
    VMyGenericInt:= TMyGenericInt.Create;
    VMyGenericInt.Value := 2014;
    VMyGenericInt.Free;
end.

2014-10-31 2:14 GMT+07:00 silvioprog :

Hm... so I'll choose the mode delphi in my new projects to type less code hehe...

Thanks guy! =)

Hm... so I'll choose the mode delphi in my new projects to type less code

hehe...

You actually ended up typing much less using objfpc style generics. Think of how many angle brackets you would need to type in Delphi mode? And how many if the specialized type changes? ;)
Delphi generics can actually do the same (create a new type first), but objfpc enforces this.

Yes, but I had some problems to understand the generic sintax in objfpc (it is not documented). =(

For example, how to compile this code using objfpc?:

unit Core.Singleton;
{$mode delphi}
interface
type
  { TSingleton }
  TSingleton<T: class, constructor> = class(TObject)
  public
    class function GetInstance: T;
  end;
implementation

{ TSingleton }

class function TSingleton<T>.GetInstance: T;
begin
  { TODO: implement! }
end;
end.

If I try to use mode objfpc:

unit Core.Singleton;
{$mode objfpc}{$H+}
interface
type
  { TSingleton }
  generic TSingleton<T: class, constructor> = class(TObject)
  public
    class function GetInstance: T;
  end;
implementation

{ TSingleton }

class function TSingleton<T>.GetInstance: T;
begin
  { TODO: implement! }
end;
end.

The error is:

Compile Project, Target: project1.exe: Exit code 1, Errors: 1
Core.Singleton.pas(11,32) Error: Illegal expression.

=(

Oh, sorry. Just:

unit Core.Singleton;
{$mode objfpc}{$H+}
interface
type
  { TSingleton }
  generic TSingleton<T: class> = class(TObject)
  public
    class function GetInstance: T;
  end;
implementation

{ TSingleton }

class function TSingleton.GetInstance: T;
begin
end;
end.

And compiled like a charm. =)

Yes, since the ObjFPC dialect was developed without type overloading in mind (in Delphi (and FPC's mode Delphi) you can have TSingleton<T> and TSingleton<T, S> in the same unit) it was decided that it is not necessary to add the <T> at the definiton of the method as well.

Regards,
Sven

Awesome. =)

Awesome. =)

It is, though the syntax is still evolving, but initial decision about <T> is what interests me as it differs a lot from C++. Delphi syntax seems to copy from C++ as is.