[fpc-devel] Generic helpers

[Hairy Pixels via fpc-devel]

Hey  guys, I was thinking about how nice generic type helpers would be today 
and remembered I did a mostly functional branch over 6 months ago so I fixed it 
up and posted it on gitlab. There’s a nasty merge error with main I need to fix 
but you can test it anyways.

For the helper type I supported: single types, dynamic arrays, static arrays, 
sets and classes and records.

Is this acceptable how I did it? I never know. :)

The main strange thing is supported compound types in helper types (like “array 
of T” or "generic TMyHelper<T> = class helper for specialize TMyClass<T>” for 
specialized generic classes/records) but I argue these are necessary for the 
feature to be complete.

https://gitlab.com/genericptr/free-pascal/-/commits/generic_helpers

For example with simple types:

=====================

program tgenhelper1;

type
  generic TMyHelper<T> = type helper for T
    procedure Print;
  end;
  TIntHelper = specialize TMyHelper<Integer>;

procedure TMyHelper.Print;
begin
  writeln(self);
end;

var
  i: integer = 100;
begin
  i.Print;
end.

=====================

Or dynamic arrays:

=====================

program tgenhelper2;

type
  generic TArrayHelper<T> = type helper for array of T
    function Count: integer;
  end;
  TIntegerArrayHelper = specialize TArrayHelper<Integer>;

function TArrayHelper.Count: integer;
begin
  result := Length(self);
end;

var
  a: array of integer;
begin
  a := [1,2,3];
  writeln(a.Count); // array of T is compatible with TIntegerArrayHelper
end.

=====================

Or classes:

=====================

program tgenhelper4;

type
  generic TMyHelper<T: class> = class helper for T
    procedure Print;
  end;
  TObjectHelper = specialize TMyHelper<TObject>;

procedure TMyHelper.Print;
begin
  writeln(ClassName);
end;

var
  c: TObject;
begin
  c := TObject.Create;
  c.Print;
end.

=====================

Regards,
        Ryan Joseph

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