[m-users.] foreign_type confusion on how to do it across modules...

[Julian Fondren]

On 2019-07-13 17:53, emacstheviking wrote:
> In my sdl2.m module I have this code
> 
>     % SDL_Rect
> :- type sdl_rect.
> :- pragma foreign_type("C", sdl_rect, "SDL_Rect",
> [can_pass_as_mercury_type]).
> 
> The SDL_Rect structure is perfect enough and I don't want to define
> something like:
> 
> :- TYPE SDL_RECT ---> SDL_RECT(X::INT, Y::INT, W::INT, H::INT).
> 
> all over the place. The compiler seems to be happy with the fact that
> when I type "sdl_rect" I will get "SDL_Rect" but in my test module I
> just can't figure out how to create an instance of it to actually pass
> atound!

Since it's abstract to Mercury, Mercury can't make instances.

Mercury can still pass four ints to a foreign_proc function that
returns an sdl_rect however.

>   SDL_RENDERFILLRECT(RND, SDL_RECT(0, 50, 200, 100), !IO),
> 
> So...given I have declared an abstract type "sdl_rect" which is
> SDL_Rect under the hood....I can't believe I am even asking this as I
> have a horrible feeling the answer is so
> obvious......whataver....better to ask!
> 
> Thanks.
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