Error about @disabled constructor when there is a custom one

[Dmitry Olshansky]

22-Jan-2013 22:45, Minas Mina пишет:
> I have this structure:
>
> struct Scene
> {
>      Array!Surface objects;    // objects in the scene
>      Array!Light lights;        // lights in the scene
>
>      /*private*/ BVHNode root;            // root node of the BVH tree
>
>      @disable this(); // disable the default constructor because space
> needs to be reserved for objects and lights
>
>      this(size_t objectReserveSpace = 20, size_t lightReserveSpace = 3)
>      {
>          objects.reserve(objectReserveSpace);
>          lights.reserve(lightReserveSpace);
>      }
> }
>
>
>
> auto scene = Scene(); // error about @disabled constructor

That is the reason I dislike D's struct constructors as they currently 
stand. Behold as the above is always rewritten to:

auto scene = Scene.init;

that is the same as

Scene scene;

And for Scene.init to work it has to have T.init for all of its members.

You've hit what I think is the design bug w.r.t. conflating 0-argument 
constructor (including one with all default args) and T.init.

Short answer is: use static opCall instead. In the meantime let us all 
pray some supreme gods so that 0-arg constructor support is introduced 
later on. (because opCall doesn't have some powers of constructors such 
as constructing const object)

> Yes, the default constructor is @disabled BUT I am not using that one. I
> want to use the other one - the custom constructor. I guess it signals
> an error because it has those defaults parameters. But shouldn't the
> compiler choose that one?

The official stance seems to be that the code shouldn't compile i.e. 
accepts-invalid.

http://d.puremagic.com/issues/show_bug.cgi?id=3438


-- 
Dmitry Olshansky