[fpc-pascal] Feature announcement: Generic functions, procedures and methods

[Anthony Walter]

Here are a few tests ...

Test 1 works:

function Swap<T>(var A, B: T): T;
var
  C: T;
begin
  C := A;
  A := B;
  B := C;
end;

Example 1 usage:

Swap<Integer>(I, J); // J now holds I value, I value holds J

Test 2 works but with notes:

function Find<T>: T;
var
  I: Integer;
begin
  for I := 0 to Form1.ComponentCount - 1 do
  if Form1.Components[I].InheritsFrom(T) then
  Exit(T(Form1.Components[I]));
  Result := nil;
end;

Example 2 usage:

Find<TShape>.Brush.Color := clRed;

Notes:

Cannot use 'as' or 'is' operators. I had to use

  if Form1.Components[I].InheritsFrom(T) then
  Exit(T(Form1.Components[I]));

Instead of

  if Form1.Components[I] is T then
  Exit(Form1.Components[I] as T);

I could not use this as a method, for example:

function TForm1.Find<T>: T;

Question:

Will it be possible to use type constraints?

function TForm1.Find<T: TComponent>: T;
or
function Find<T: TComponent>: T;

Test 3 does not work:

function Compare<T>(constref A, B: T): Integer;
begin
  if A > B then
    Result := 1
  else if B > A then
  Result := -1
  else
    Result := 0;
end;

procedure Test3;
var
  Items: TArrayList<Single>; // See Codebot.System
begin
  Randomize;
  Items.Push(Random * 100);
  Items.Push(Random * 100);
  Items.Push(Random * 100);
  Items.Push(Random * 100);
  // compile fails below
  Items.Sort(soDescend, @Compare<Single>); // cannot take address of
Compare<Single>
end;
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