Casting a parent-member function template argument to a child-member one

[bstani...@gmail.com]

Hello,

I want to make sure that I'm reading this correctly as an issue in the standard before posting to w...@edg.com . It could be that I've misunderstood the wording and this is in fact a bug in multiple compilers and not an issue with the standard.

The long story is this blog post of mine: https://ibob.github.io/blog/2018/08/18/a-bug-in-the-cpp-standard/

The short story is that this does not compile with gcc and clang and -std=c++17 (it does compile with msvc but it is not a staple of standard conformance): https://godbolt.org/z/6NQEU_

Basically I want to set a function of type (parent::*) as a template argument of a function which expects (child::*). There exists an implicit cast between those types. However even when explicitly casting the template argument to (child::*) neither gcc nor clang manage to compile it.

It suspect that the issue is in this text: "If the template-argument represents a set of overloaded functions (or a pointer or member pointer to such), the matching function is selected from the set (13.4)."  from N4198

Thanks,
Borislav

[Richard Smith]

On Sun, 19 Aug 2018, 08:44 , <bstani...@gmail.com> wrote:

Hello,

I want to make sure that I'm reading this correctly as an issue in the standard before posting to w...@edg.com . It could be that I've misunderstood the wording and this is in fact a bug in multiple compilers and not an issue with the standard.

The long story is this blog post of mine: https://ibob.github.io/blog/2018/08/18/a-bug-in-the-cpp-standard/

The short story is that this does not compile with gcc and clang and -std=c++17 (it does compile with msvc but it is not a staple of standard conformance): https://godbolt.org/z/6NQEU_

Basically I want to set a function of type (parent::*) as a template argument of a function which expects (child::*). There exists an implicit cast between those types. However even when explicitly casting the template argument to (child::*) neither gcc nor clang manage to compile it.

The code is valid, but the Itanium C++ ABI does not specify a mangling for it yet, so compilers targeting that ABI tend to not accept it yet. Clang produces a "sorry, not supported yet" error if you try this with a class template, but unfortunately you only get a generic "bad template arguments" error in the function template case.

It suspect that the issue is in this text: "If the template-argument represents a set of overloaded functions (or a pointer or member pointer to such), the matching function is selected from the set (13.4)."  from N4198

Thanks,
Borislav

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