AnyHash.h

#ifndef ANY_HASH_H
#define ANY_HASH_H

#ifdef _MSC_VER
# include <iso646.h>
#endif 

#include <functional>
#include <cstddef>
#include <type_traits>

namespace te {

template <class T = void>
struct Hash: std::hash<T>
{

};

namespace detail {

template <class T>
struct has_hash_specialization: 
    std::conditional_t<
        std::is_default_constructible_v<Hash<T>>,
        std::true_type,
        std::false_type
    > 
{

};

template <class T>
inline constexpr const bool has_hash_specialization_v = has_hash_specialization<T>::value;

} /* namespace detail */



template <>
struct Hash<void>
{
    template <class T>
    std::size_t operator()(const T& value) const
    { return std::invoke(Hash<T>{}, value); }
};

template <class T, class = std::enable_if_t<detail::has_hash_specialization_v<T>>>
std::size_t hash_value(const T& value)
{ return std::invoke(Hash<T>{}, value); }

struct AnyHash {

    template <class T>
    std::size_t operator()(const T& value) const
    {
        using te::hash_value;
        return hash_value(value);
    }
};

} /* namespace te */

#endif /* ANY_HASH_H */