[Bug c++/48617] New: [C++0x] Problem with non-type template parameters and decltype

[Bug c++/48617] New: [C++0x] Problem with non-type template parameters and decltype

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48617

           Summary: [C++0x] Problem with non-type template parameters and
                    decltype
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: daniel.kruegler@googlemail.com


gcc 4.7.0 in C++0x mode rejects the following program:

//---------------
template<class T, decltype(T())> // #
struct A {};

A<int, 0> a;

int main() {}
//---------------

The error message annotated at line # is:

"error: 'decltype (T())' is not a valid type for a template constant parameter"

It seems to me that according to the FDIS this should be well-formed program:
decltype is feasible as a /parameter-declaration/. The new type-equivalence
rules in [temp.type] p. 2,

"If an expression e involves a template parameter, decltype(e) denotes a unique
dependent type. Two such decltype-specifiers refer to the same type only if
their expressions are equivalent (14.5.6.1)."

should allow for a compiler to deduce the meaning similar to other dependent
contexts. See also [temp.dep.type] p. 8 for this matter:

"A type is dependent if it is [...] denoted by decltype(expression), where
expression is type-dependent (14.6.2.2)."

[Bug c++/48617] [C++0x] Problem with non-type template parameters and decltype

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48617

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2011.05.22 19:01:54
                 CC|                            |jason at gcc dot gnu.org
         AssignedTo|unassigned at gcc dot       |jason at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

[Bug c++/48617] [C++0x] Problem with non-type template parameters and decltype

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48617

--- Comment #1 from Jason Merrill <jason at gcc dot gnu.org> 2011-05-23 15:32:13 UTC ---
Author: jason
Date: Mon May 23 15:32:10 2011
New Revision: 174070

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=174070
Log:
    PR c++/48617
    * pt.c (invalid_nontype_parm_type_p): Allow DECLTYPE_TYPE.

Added:
    trunk/gcc/testsuite/g++.dg/cpp0x/decltype27.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/pt.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/48617] [C++0x] Problem with non-type template parameters and decltype

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48617

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> 2011-05-25 01:08:10 UTC ---
Author: jason
Date: Wed May 25 01:08:07 2011
New Revision: 174158

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=174158
Log:
    PR c++/48617
    * pt.c (invalid_nontype_parm_type_p): Allow DECLTYPE_TYPE.

Added:
    branches/gcc-4_6-branch/gcc/testsuite/g++.dg/cpp0x/decltype27.C
Modified:
    branches/gcc-4_6-branch/gcc/cp/ChangeLog
    branches/gcc-4_6-branch/gcc/cp/pt.c
    branches/gcc-4_6-branch/gcc/testsuite/ChangeLog

[Bug c++/48617] [C++0x] Problem with non-type template parameters and decltype

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48617

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.6.1

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> 2011-05-25 01:20:09 UTC ---
Fixed for 4.6.1.

[Bug c++/48617] [C++0x] Problem with non-type template parameters and decltype

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48617

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jwakely.gcc at gmail dot
                   |                            |com

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> 2011-06-18 19:15:09 UTC ---
*** Bug 43646 has been marked as a duplicate of this bug. ***