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Subject: Re: Why does overload resolution fail in this simple case?
From: Vishal Oza (vickoza_at_[hidden])
Date: 2020-12-29 19:03:44


it looks like it compiles on icc my guess is that is does not know what
type of reference it is and should use

On Tue, Dec 29, 2020 at 3:04 PM Hani Deek via Std-Discussion <
std-discussion_at_[hidden]> wrote:

> Hello,
>
>
> With MSVC, the following code compiles. The char overload is selected by
> overload resolution.
>
> struct S
> {
> operator int() const & { return 0; }
> operator char() && { return 0; }
> };
>
> void foo(int) {}
> void foo(char) {}
>
> int main()
> {
> foo(S{}); //OK, calls 'void foo(char)'.
> }
>
> However, the following code won't compile.
>
> struct S
> {
> int i = 0;
> operator const int &() const & { return i; }
> operator int &&() && { return (int &&)(i); }
> };
>
> void foo(const int &) {}
> void foo(int &&) {}
>
> int main()
> {
> foo(S{}); //error C2668: 'foo': ambiguous call to overloaded function
> //message : could be 'void foo(int &&)'
> //message : or 'void foo(const int &)'
> }
>
> What is exactly the difference that makes the second sample fail to
> compile?
>
> Given that 'operator int &&() &&' is an exact match to the conversion
> required to call 'void foo(int &&)', I expected the compiler to select
> it. It is strange if the C++ rules will not allow the compiler to select a
> conversion function that exactly matches the required conversion, both in
> terms of the provided argument 'S &&' and the result of conversion 'int &&
> '.
>
> --
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> Std-Discussion_at_[hidden]
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>



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