[Issue 11722] Qualifier-only casts should not invoke opCast

[d-bugmail at puremagic.com]

https://d.puremagic.com/issues/show_bug.cgi?id=11722



--- Comment #6 from Kenji Hara <k.hara.pg at gmail.com> 2013-12-12 23:44:33 PST ---
(In reply to comment #5)
> (In reply to comment #0)
> > This is a spin-off issue from bug 5747.
> > 
> > D has a cast syntax for modifying just only the type qualifier of the operand.
> > 
> > http://dlang.org/expression#CastExpression
> > 
> > CastExpression:
> >     cast ( Type ) UnaryExpression
> >     cast ( CastQual ) UnaryExpression   <--
> >     cast ( ) UnaryExpression            <--
> 
> Kenji: I'm wondering: Your original post seemed to imply the enhancement was
> *only* for qualifier cast. However, the final result seems to be for *any* kind
> of cast, whith matching types. I mean:
> 
> const(S) s;
> auto a = cast() s;
> auto b = cast(S) s;
> 
> In the case of "a": We have a "CastQual" type cast, and this bypasses the
> opCast operator entirelly.
> In the case of "b": We have a *Type* cast, but that happens to result only in a
> qualifier change.
> 
> In the case of "b", *should* we call opCast? Please clarify.

Yes.
And actually, with git-head, following code asserts only in the case of "b".

struct S {
    T opCast(T)() const { assert(0); }
}
void main()
{
    const(S) s;
    auto a = cast() s;  // bypass opCast
    auto b = cast(S) s; // call opCast and assert
}

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