http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52440
Bug #: 52440
Summary: [C++11] Wrong template argument deduction/substitution
failures
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: ai.az...@gmail.com
Created attachment 26790
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26790
Output of -v option and preprocessed file
I can't find anything to prevent the following code from compiling;
/////////////////////////////////////////////////////////
template<bool>
struct V
{
typedef void type;
};
template<typename T>
struct X
{
template<typename>
static constexpr bool always_true()
{
return true;
};
template<typename U,
typename = typename V<always_true<U>()>::type>
X(U &&) {} // Line 18
};
int main()
{
X<int> x(42); // Line 23
}
/////////////////////////////////////////////////////////
However, GCC complains about deduction/substitution failure;
main.cpp: In function 'int main()':
main.cpp:23:14: error: no matching function for call to 'X<int>::X(int)'
main.cpp:23:14: note: candidates are:
main.cpp:18:3: note: template<class U, class> X::X(U&&)
main.cpp:18:3: note: template argument deduction/substitution failed:
main.cpp:8:8: note: constexpr X<int>::X(const X<int>&)
main.cpp:8:8: note: no known conversion for argument 1 from 'int' to 'const
X<int>&'
main.cpp:8:8: note: constexpr X<int>::X(X<int>&&)
main.cpp:8:8: note: no known conversion for argument 1 from 'int' to
'X<int>&&'
The constructor template in line 18 should always succeed in template argument
deduction/substitution and be used for the invocation in Line 23.
My guess is that this is a bug of GCC.
