http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56387
Bug #: 56387
Summary: Alias of class template wrongly seen as different
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: pk...@outlook.com
Created attachment 29490
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29490
Minimal test case
The attached minimal test case creates an alias template of a variadic class
template. A function foo2 fails to unify a template template parameter C when
given two arguments created using both forms - but only if the object created
using the alias template is passed to a parameter expecting a reference. An
online 4.8.0 compiler also failed.
g++ -c -std=c++11 -Wall -Wextra gcc472templatetemplatebug.cpp
The code and error are also listed below:
template <int ...Is>
struct is1 {};
template <int ...Is>
using is2 = is1<Is...>;
template <template <int ...> class C, int ...Is, int ...Js>
void foo1(C<Is...> a, C<Js...> b) {}
template <template <int ...> class C, int ...Is, int ...Js>
void foo2(C<Is...> a, C<Js...> &b) {} // !
void test()
{
is1<1,2,345> x;
is2<6,78,90> y;
foo1(x,y);
foo2(x,y);
}
// Now the error messages:
cc472templatetemplatebug.cpp: In function ‘void test()’:
gcc472templatetemplatebug.cpp:18:11: error: no matching function for call to
‘foo2(is1<1, 2, 345>&, is2<6, 78, 90>&)’
gcc472templatetemplatebug.cpp:18:11: note: candidate is:
gcc472templatetemplatebug.cpp:11:6: note: template<template<int ...<anonymous>
> class C, int ...Is, int ...Js> void foo2(C<Is ...>, C<Js ...>&)
gcc472templatetemplatebug.cpp:11:6: note: template argument
deduction/substitution failed:
gcc472templatetemplatebug.cpp:18:11: note: deduced conflicting types for
parameter ‘C<Js ...>’ (‘template<int ...Is> struct is1’ and ‘template<int .
..Is> using is2 = is1<Is ...>’)
gcc472templatetemplatebug.cpp: In instantiation of ‘void foo1(C<Is ...>, C<Js
...>) [with C = is1; int ...Is = {1, 2, 345}; int ...Js = {6, 78, 90}]’:
gcc472templatetemplatebug.cpp:17:11: required from here
gcc472templatetemplatebug.cpp:8:6: warning: unused parameter ‘a’
[-Wunused-parameter]
gcc472templatetemplatebug.cpp:8:6: warning: unused parameter ‘b’
[-Wunused-parameter]
