Dynamic array of pointers to opaque structs

[Johan F.]

I'm fiddling around with SDL2 using Derelict3, and I'm trying to 
make an array of SDL_Texture pointers, like so:

     SDL_Texture*[] frames;
     ... make texture ...
     frames ~= texture;

However, this yields the following error:

/Users/jaffe1/prog/Derelict3/import/derelict/sdl2/types.d(1865): 
Error: struct derelict.sdl2.types.SDL_Texture is forward 
referenced when looking for 'toHash'
/Users/jaffe1/prog/Derelict3/import/derelict/sdl2/types.d(1865): 
Error: struct derelict.sdl2.types.SDL_Texture is forward 
referenced when looking for 'opCmp'
/Users/jaffe1/prog/Derelict3/import/derelict/sdl2/types.d(1865): 
Error: struct derelict.sdl2.types.SDL_Texture is forward 
referenced when looking for 'toString'
/Users/jaffe1/prog/Derelict3/import/derelict/sdl2/types.d(1865): 
Error: struct derelict.sdl2.types.SDL_Texture unknown size
/Users/jaffe1/prog/Derelict3/import/derelict/sdl2/types.d(1865): 
Error: struct derelict.sdl2.types.SDL_Texture no size yet for 
forward reference
/Users/jaffe1/prog/Derelict3/import/derelict/sdl2/types.d(1865): 
Error: struct derelict.sdl2.types.SDL_Texture unknown size
/Users/jaffe1/prog/Derelict3/import/derelict/sdl2/types.d(1865): 
Error: struct derelict.sdl2.types.SDL_Texture no size yet for 
forward reference

At line 1865 in types.d is the opaque struct declaration

     struct SDL_Texture;

The program compiles and works fine if I change this line to

     struct SDL_Texture {};

This seems weird to me. Why is making an array of _pointers_ to 
SDL_Texture dependant on how the SDL_Texture struct is declared? 
Also, is simply adding {} the right way of fixing it, or will 
that possibly break something else?