Style: Do we really need typed aliases?

[Free-Pascal-meets-SDL-Website]

Hey @suve and all,

I wonder if the effort to translate all the types of SDL3 to typed aliases is worth it. Most types of SDL3 are integer types. These and their typed aliases are assignment-compatible in Free Pascal and Delphi, so usually nobody will ever find out that he used the "wrong" type on, e. g. calling a function, unless specifically a type check is performed (by the caller).

Am I missing anything?

Best regards
Matthias

[suve]

Huh. I somehow missed the fact that doing type X = type integer; still retains assignment-compatibility. Despite that, I think that using the type type syntax doesn't hurt, as the "cost" is just typing some 5 extra chars, and it allows for custom function overloads, which may be useful for some.

[Free-Pascal-meets-SDL-Website]

Huh. I somehow missed the fact that doing type X = type integer; still retains assignment-compatibility.

I wasn't sure before, too. To check if this is indeed true, I made the following test though:

program project1;

uses
  TypInfo;

type
  TTypeA = type Integer;
  TTypeB = type Integer;

function MultiplyTypeA(A: TTypeA; B: TTypeA): TTypeA;
begin
  Result:=A*B;
end;

function MultiplyTypeB(A: TTypeB; B: TTypeB): TTypeB;
begin
  Result:=A*B;
end;

var
  IntA1, IntA2: TTypeA;
  IntB1, IntB2: TTypeB;
  Int: Integer;

begin
  IntA1 := 2;
  IntA2 := 3;
  IntB1 := 4;
  IntB2 := 5;
  Int := 6;

  Writeln('Use correct types as arguments:');
  Writeln(MultiplyTypeA(IntA1, IntA2));
  Writeln(MultiplyTypeB(IntB1, IntB2));

  Writeln('Use WRONG types as arguments:');
  Writeln(MultiplyTypeA(IntB1, IntB2));
  Writeln(MultiplyTypeB(IntA1, IntA2));

  Write('A1 and A2 are...');
  if TypeInfo(IntA1) = TypeInfo(IntA2) then
    writeln('equal')
  else
    writeln('unequal');

  Write('A1 and B1 are...');
  if TypeInfo(IntA1) = TypeInfo(IntB1) then
    writeln('equal')
  else
    writeln('unequal');

  Write('B1 and B2 are...');
  if TypeInfo(IntB1) = TypeInfo(IntB2) then
    writeln('equal')
  else
    writeln('unequal');

  Write('A1 and Integer are...');
  if TypeInfo(IntA1) = TypeInfo(Int) then
    writeln('equal')
  else
    writeln('unequal');
end.

It will compile and the multiply functions will work with whatever type you use.

Back to our translation:
It is not the 5 extra chars in the type-part which is the extra effort. But the effort is necessary in the const-part to type the allowed values, e. g.:

type
  PPSDL_PixelType = ^PSDL_PixelType;
  PSDL_PixelType = ^TSDL_PixelType;
  TSDL_PixelType = type Integer;

const
  SDL_PIXELTYPE_UNKNOWN = TSDL_PixelType(0);
  SDL_PIXELTYPE_INDEX1 = TSDL_PixelType(1);
  SDL_PIXELTYPE_INDEX4 = TSDL_PixelType(2);
  SDL_PIXELTYPE_INDEX8 = TSDL_PixelType(3);
  SDL_PIXELTYPE_PACKED8 = TSDL_PixelType(4);
  SDL_PIXELTYPE_PACKED16 = TSDL_PixelType(5);
  SDL_PIXELTYPE_PACKED32 = TSDL_PixelType(6);
  SDL_PIXELTYPE_ARRAYU8 = TSDL_PixelType(7);
  SDL_PIXELTYPE_ARRAYU16 = TSDL_PixelType(8);
  SDL_PIXELTYPE_ARRAYU32 = TSDL_PixelType(9);
  SDL_PIXELTYPE_ARRAYF16 = TSDL_PixelType(10);
  SDL_PIXELTYPE_ARRAYF32 = TSDL_PixelType(11);
  { appended at the end for compatibility with sdl2-compat:   }
  SDL_PIXELTYPE_INDEX2 = TSDL_PixelType(12);

All values have to be specified to be of this new type. I mean, there is the search-and-replace tool in Lazarus IDE, but still it is an extra effort considering the amount of these types in the SDL3 headers.

and it allows for custom function overloads, which may be useful for some.

Could you give a quick example, please? This may be a benefit.