[fpc-pascal] Re: generics question

[leledumbo]

Err... because at the time, T is not yet known. It would still fail to
compile even if you don't do any specialization. I guess the compiler does
type checking while parsing the generic class (and its methods) declaration,
not while specializing (well... it would still do type checking when
specializing, but the error would be a little cryptic due to missing exact
error location).

IMHO a solution would be to have additional compile-time syntax to check the
type of T (but this may cause a lot of headache due to inheritance concept).
Since it's impossible with the current state, the current solution would be
to declare a procedural type (with T as argument) inside the generic class
and instead of calling blah directly make it a procedural variable of that
type as argument of Test (since it's a class function). The caveat is of
course you have to pass Blah all the time. But unfortunately... it doesn't
work as well :(

Here's your modified program (compiled, but just run and see its output):

{$mode delphi}

uses
  SysUtils;


function Blah(const val: Integer): string; inline; overload;
begin
  Result:= IntToStr(val + 1);
end;

function Blah(const val: string): string; inline; overload;
begin
  Result:= val + '1';
end;

type
  TTestGen<T> = class
  type
    TBlah = function (const val: T): string;
  public
    constructor Create();
    class function Test(val: T; ABlah: TBlah): string; inline;
  end;

{ TTestGen }

constructor TTestGen<T>.Create();
begin
end;

class function TTestGen<T>.Test(val: T; ABlah: TBlah): string;
begin
  Result:= ABlah(val);
end;


type
  TTestInt = TTestGen<Integer>;
  TTestString = TTestGen<String>;

begin
  WriteLn(TTestInt.Test(1, at Blah));
  WriteLn(TTestString.Test('test', at Blah));
end.

If I don't overload Blah and pass the correct function for each call, then
the result is correct. Somebody's gotta file a bug report.

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