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### 920. Ref-qualification support in the library

Section: 20.14.16 [func.memfn] Status: C++11 Submitter: Bronek Kozicki Opened: 2008-10-06 Last modified: 2016-01-28

Priority: Not Prioritized

View all other issues in [func.memfn].

View all issues with C++11 status.

Duplicate of: 1230

Discussion:

Daniel Krügler wrote:

> Shouldn't above list be completed for &- and &&-qualified member functions This would cause to add:

> >     template<Returnable R, class T, CopyConstructible... Args>
> >     unspecified mem_fn(R (T::* pm)(Args...) &);
> >     template<Returnable R, class T, CopyConstructible... Args>
> >     unspecified mem_fn(R (T::* pm)(Args...) const &);
> >     template<Returnable R, class T, CopyConstructible... Args>
> >     unspecified mem_fn(R (T::* pm)(Args...) volatile &);
> >     template<Returnable R, class T, CopyConstructible... Args>
> >     unspecified mem_fn(R (T::* pm)(Args...) const volatile &);
> >     template<Returnable R, class T, CopyConstructible... Args>
> >     unspecified mem_fn(R (T::* pm)(Args...) &&);
> >     template<Returnable R, class T, CopyConstructible... Args>
> >     unspecified mem_fn(R (T::* pm)(Args...) const &&);
> >     template<Returnable R, class T, CopyConstructible... Args>
> >     unspecified mem_fn(R (T::* pm)(Args...) volatile &&);
> >     template<Returnable R, class T, CopyConstructible... Args>
> >     unspecified mem_fn(R (T::* pm)(Args...) const volatile &&);

yes, absolutely. Thanks for spotting this. Without this change `mem_fn` cannot be initialized from pointer to ref-qualified member function. I believe semantics of such function pointer is well defined.

[ Post Summit Daniel provided wording. ]

[ Batavia (2009-05): ]

> We need to think about whether we really want to go down the proposed path of combinatorial explosion. Perhaps a Note would suffice.

> We would really like to have an implementation before proceeding.

> Move to Open, and recommend this be deferred until after the next Committee Draft has been issued.

[ 2009-10-10 Daniel updated wording to post-concepts. ]

> 1230 has a similar proposed resolution

[ 2009-10 Santa Cruz: ]

> Move to Ready.

Proposed resolution:

1. Change 20.14 [function.objects]/2, header `<functional>` synopsis as follows:

   >     // 20.7.14, member function adaptors:
   >     template<class R, class T> unspecified mem_fn(R T::*);

   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...));
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) const);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) volatile);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) const volatile);

   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) &);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) const &);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) volatile &);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) const volatile &);

   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) &&);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) const &&);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) volatile &&);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::*)(Args...) const volatile &&);

2. Change the prototype list of 20.14.16 [func.memfn] as follows [NB: The following text, most notably p.2 and p.3 which discuss influence of the cv-qualification on the definition of the base class's first template parameter remains unchanged. ]:

   >     template<class R, class T> unspecified mem_fn(R T::* pm);

   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...));
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) volatile);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const volatile);

   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) &);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const &);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) volatile &);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const volatile &);

   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) &&);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const &&);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) volatile &&);
   >     template<class R, class T, class ...Args> unspecified mem_fn(R (T::* pm)(Args...) const volatile &&);

3. Remove 20.14.16 [func.memfn]/5:

   > Remarks: Implementations may implement `mem_fn` as a set of overloaded function templates.