Mismatch overload problem
Why does s have the value false?
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template<typename T> char test_have_range(decltype(&T::begin), decltype(&T::end));
template<typename T> short test_have_range(...);
constexpr bool s = sizeof(test_have_range<list<int>>(0,0)) == sizeof(char);
static_assert(s);
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Regards,
Juan
Last edited on
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#ifndef DUTHOMHAS_IS_ITERABLE_HPP
#define DUTHOMHAS_IS_ITERABLE_HPP
// SFINAE check to see if class can be used with begin() and end()
// Copyright 2017 Michael Thomas Greer
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file ../../LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt )
#include <iterator>
#include <type_traits>
#include <utility>
namespace duthomhas
{
//-----------------------------------------------------------------------------------------------
// is_iterable <T> ::value
//-----------------------------------------------------------------------------------------------
// The basis for this code was found at
// https://stackoverflow.com/a/29634934/2706707
//
namespace is_iterable_internal
{
using std::begin;
using std::end;
template <typename T>
class is_iterable
{
template <typename U>
static constexpr auto is_iterable_impl( int )
-> decltype(
begin( std::declval <U&> () ) != end( std::declval <U&> () ), // begin/end and operator !=
void(), // Handle evil operator ,
++std::declval <decltype( begin( std::declval <U&> () ) )&> (), // operator ++
void( *begin( std::declval <U&> () ) ), // operator*
std::true_type {}
)
{ return std::true_type {}; }
template <typename U>
static constexpr std::false_type is_iterable_impl(...)
{ return std::false_type {}; }
typedef decltype( is_iterable_impl <T> ( 0 ) ) type;
public:
#if __cplusplus < 201402L
enum : bool { value = type::value };
#else
static constexpr bool value = type::value;
#endif
};
}
template <typename T>
using is_iterable = is_iterable_internal::is_iterable <T> ;
}
#endif
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