Hello,

I'm trying to add new features in a third generic type. Please see this simulation below:

{ TThirdGeneric }

  generic TThirdGeneric<T> = class
  private
    FFoo: T;
  public
    procedure Post;
    property Foo: T read FFoo;
  end;
  { TMyGeneric }
  generic TMyGeneric<T> = class(TThirdGeneric)
  public
    procedure ConfigureFoo;
  end;
  { TMyClass }
  TMyClass = class(TMyGeneric)
  public
    procedure Post;
  end;

...

{ TMyGeneric }

procedure TMyGeneric.ConfigureFoo;
begin
  ... pre configure Foo ...
end;

{ TMyClass }

procedure TMyClass.Post;
begin
  Write(Foo.AProperty); // using pre configured Foo
end;

Just trying to understand the generics concept correctly. :S

This must be "class(specialize TThirdGeneric<T>)" (the "T" is the same type parameter as specified for the "TMyGeneric" declaration, so if it would be "TMyGeneric<MyType>" it would need to be "class(specialize TThirdGeneric<MyType>)")

A class parent must always be a specialization as generics are no valid types per se. So here the correct declaration would again be "class(specialize TMyGeneric<WhateverTypeYouNeed>)".

public procedure Post; end;

[snip]

Just trying to understand the generics concept correctly. :S

Regards,
Sven

2014-02-26 13:28 GMT-03:00 Sven Barth :

Compiled like a charm. I'm loving it. Very very nice!

So, I'll implement some methods in a descendant type of this class:

https://github.com/silvioprog/brookframework/blob/master/core/brookaction.pas#L262

then:

  TjTableEditAction = (eaList, eaCreate, eaUpdate, eaDelete);
  { TjTableEntityAction }

generic TjTableEntityAction<T> = class(specialize TBrookEntityAction<T>)

  public
    { TODO: implement jTable paging -

http://www.jtable.org/apireference#genopt-paging } { TODO: implement jTable edit action -
http://www.jtable.org/apireference#Actions }

  end;

And generics will be very helpful in this task.

Thank you again Sven! (y)

ps. is there any complete documentation about generics in Free Pascal? The Lazarus wiki is a bit incomplete.

2014-02-26 16:15 GMT-03:00 silvioprog :

2014-02-26 13:28 GMT-03:00 Sven Barth :

[...]

Generics power:

https://raw.github.com/silvioprog/dopf/master/demos/entity/demo1.lpr

Soon, I'll:

storage.Entity.Id := 3;
storage.Entity.Name := 'Sven';
storage.Save; // storing entity ...
storage.Modify; // modifying
storage.Move(NewEntity); // moving entity ...
...
for Person in storage.List.Entities do
  WriteLn('ID: ', Person.Id, ' Name: ', Person.Name);

ie. without SQL, but also allowing user to use a specific SQL (link SQL with joins).

Thanks Joao and Sven!

silvioprog wrote

Thank you again Sven! (y)

You're welcome.

ps. is there any complete documentation about generics in Free Pascal? The Lazarus wiki is a bit incomplete.

There is a section inside the language reference guide, but this even reflects only pre-2.6 state. So this will need a major overhaul when 2.8/3.0 is released. :)

Regards,
Sven