[Bug c++/66766] New: Reference to an “auto” function as a template parameter

[Bug c++/66766] New: Reference to an “auto” function as a template parameter

[quentin.c.diaz at gmail dot com]

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66766

            Bug ID: 66766
           Summary: Reference to an “auto” function as a template
                    parameter
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: quentin.c.diaz at gmail dot com
  Target Milestone: ---

The following code :

template <void (&a)()>
struct Foo {
    static auto value() {}
};

void bar() {}

template struct Foo<Foo<bar>::value>;

Causes the following error :

error: could not convert template argument ‘Foo<a>::value<bar>’ to ‘void (&)()’
 template struct Foo<Foo<bar>::value>;
                                    ^

Any of the following makes it compile successfully :
 - Declaring value() as returning void instead of deducing it
 - "Dereferencing" value : template struct Foo<*Foo<bar>::value>;
 - Parenthesizing value : template struct Foo<(Foo<bar>::value)>;
 - Making a a pointer : template <void (*a)()> struct Foo ...
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Subject: [Bug fortran/52251] Nonadvancing I/O and the t edit descriptor
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idR251

--- Comment #6 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
Created attachment 35911
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id5911&actioníit
A patch to fix this.

This patch issues the tab spacing based on spaces previously skipped pending
transfer of data.  In the test case, there is no data transferred so we were
skipping handling the skips.

[Bug c++/66766] Reference to an “auto” function as a template parameter

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66766

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
   Last reconfirmed|                            |2021-08-04
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

[Bug c++/66766] static class member function returning auto is not assignable to a function type reference

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66766

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Reference to an “auto”      |static class member
                   |function as a template      |function returning auto is
                   |parameter                   |not assignable to a
                   |                            |function type reference
   Last reconfirmed|2021-08-04 00:00:00         |2024-4-4

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced slightly more:
```
template <int>
struct Foo {
    static auto value() {}
};
void (&a)() = Foo<1>::value;
```

Note function pointers work.