[cfe-dev] [bug] Wrong overload chosen when a conversion operator to const T() exists

[John McCall]

On Oct 8, 2012, at 5:54 AM, Philipp Moeller wrote:
> the following snippet does compile on gcc 4.7.1, but fails with clang
> trunk r165389
> 
> struct Y {};
> 
> struct X {
>  operator const Y() const { return Y(); }
> };
> 
> void f(Y&& y) {}
> 
> int main()
> {
>  f(X());
>  return 0;
> }
> 
> As far as I can tell, clang is right to reject this code as it would
> require two user-defined conversion.

I believe there's something more general about not doing a
copy-construction in cases like this, but yeah, we're right to reject it.

> However, when another overload void f(const Y& y); is added clang still
> wont accept the code. This problem also appears when using standard
> library containers (vector::push_back).
> 
> Shouldn't clang choose the f(const Y&) over f(Y&&) and accept the code?

Yeah.  It looks like our overload resolution is somehow ignoring the qualifiers
here and therefore preferring the Y&& candidate, and then the actual call
fails.

Please file a bug.

John.