Variadic templates and C arrays

Question

I'm trying to compile the following piece of code:

template <typename T, int N> void foo( const T (&array)[N]) {}

template <typename T> static int args_fwd_(T const &t) { foo(t); return 0; }

template<class ...Us> void mycall(Us... args) {
    int xs[] = { args_fwd_(args)... };
}

int main(void) {
    int b[4];
    mycall(b);
}

The mycall function uses variadic templates and then forwards to the args_fwd_ function to call the function foo on each argument.

This works fine for most argument types (assuming I have appropriately defined foo functions). But when I try to pass a C-style array (int b[4]) it gets turned into a pointer and then it can't find the templated foo function that requires an array (not pointer). The error from gcc 4.9.3 is as follows:

error: no matching function for call to ‘foo(int* const&)’
note: candidate is:
note: template<class T, int N> void foo(const T (&)[N])
   template <typename T, int N> void foo( const T (&array)[N]) {}
note:   template argument deduction/substitution failed:
note:   mismatched types ‘const T [N]’ and ‘int* const’

Note the part about looking for a pointer. This is the same in clang as well so apparently this is standard compliant. Is there a way to preserve that this is a C array without it getting converted to a pointer?

Answer 1

Yes. Use perfect forwarding:

#include <utility>

template<class ...Us> void mycall(Us&&... args) {
    int xs[] = { args_fwd_(std::forward<Us>(args))... };
}