Consider the following code:
template<int N>
class Vector
{
};
#include <array>
template<int N>
void doWork(const Vector<N>&, const std::array<int,N>&)
{
}
int main()
{
std::array<int,3> arr;
Vector<3> vec;
doWork(vec,arr);
}
Here Vector
represents a class which is defined in a third-party library, and std::array
is known to take its element count as std::size_t
.
I've tried compiling this with clang-3.6 and g++-5.1. Clang worked without any complaint, while g++ gives the following error:
test.cpp: In function ‘int main()’:
test.cpp:17:19: error: no matching function for call to ‘doWork(Vector<3>&, std::array<int, 3ul>&)’
doWork(vec,arr);
^
test.cpp:9:6: note: candidate: template<int N> void doWork(const Vector<N>&, const std::array<int, N>&)
void doWork(const Vector<N>&, const std::array<int,N>&)
^
test.cpp:9:6: note: template argument deduction/substitution failed:
test.cpp:17:19: note: mismatched types ‘int’ and ‘long unsigned int’
doWork(vec,arr);
^
test.cpp:17:19: note: ‘std::array<int, 3ul>’ is not derived from ‘const std::array<int, N>’
I can work around this by doing a cast of N
to std::size_t
in second parameter of doWork()
or calling doWork<3>()
, but this wouldn't educate me.
So I rather ask first: which compiler is right here? Am I really doing something wrong in the code (so clang is too permissive), or is it indeed valid C++ (so that g++ has a bug)?
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