toml11/toml/traits.hpp

//     Copyright Toru Niina 2017.
// Distributed under the MIT License.
#ifndef TOML11_TRAITS_HPP
#define TOML11_TRAITS_HPP
#include <type_traits>
#include <utility>
#include <chrono>
#include <tuple>

namespace toml
{

class value; // forward decl

namespace detail
{

template<typename T>
using unwrap_t = typename std::decay<T>::type;

// ---------------------------------------------------------------------------
// check whether type T is a kind of container/map class

struct has_iterator_impl
{
    template<typename T> static std::true_type  check(typename T::iterator*);
    template<typename T> static std::false_type check(...);
};
struct has_value_type_impl
{
    template<typename T> static std::true_type  check(typename T::value_type*);
    template<typename T> static std::false_type check(...);
};
struct has_key_type_impl
{
    template<typename T> static std::true_type  check(typename T::key_type*);
    template<typename T> static std::false_type check(...);
};
struct has_mapped_type_impl
{
    template<typename T> static std::true_type  check(typename T::mapped_type*);
    template<typename T> static std::false_type check(...);
};
struct has_resize_method_impl
{
    constexpr static std::size_t dummy=0;
    template<typename T> static std::true_type  check(decltype(std::declval<T>().resize(dummy))*);
    template<typename T> static std::false_type check(...);
};

struct has_from_toml_method_impl
{
    template<typename T>
    static std::true_type  check(
        decltype(std::declval<T>().from_toml(std::declval<::toml::value>()))*);
    template<typename T>
    static std::false_type check(...);
};
struct has_into_toml_method_impl
{
    template<typename T>
    static std::true_type  check(decltype(std::declval<T>().into_toml())*);
    template<typename T>
    static std::false_type check(...);
};

/// Intel C++ compiler can not use decltype in parent class declaration, here
/// is a hack to work around it. https://stackoverflow.com/a/23953090/4692076
#ifdef __INTEL_COMPILER
#define decltype(...) std::enable_if<true, decltype(__VA_ARGS__)>::type
#endif

template<typename T>
struct has_iterator    : decltype(has_iterator_impl::check<T>(nullptr)){};
template<typename T>
struct has_value_type  : decltype(has_value_type_impl::check<T>(nullptr)){};
template<typename T>
struct has_key_type    : decltype(has_key_type_impl::check<T>(nullptr)){};
template<typename T>
struct has_mapped_type : decltype(has_mapped_type_impl::check<T>(nullptr)){};
template<typename T>
struct has_resize_method : decltype(has_resize_method_impl::check<T>(nullptr)){};


template<typename T>
struct has_from_toml_method
: decltype(has_from_toml_method_impl::check<T>(nullptr)){};
template<typename T>
struct has_into_toml_method
: decltype(has_into_toml_method_impl::check<T>(nullptr)){};

#ifdef __INTEL_COMPILER
#undef decltype(...)
#endif

// ---------------------------------------------------------------------------
// C++17 and/or/not

template<typename ...> struct conjunction : std::true_type{};
template<typename T>   struct conjunction<T> : T{};
template<typename T, typename ... Ts>
struct conjunction<T, Ts...> :
    std::conditional<static_cast<bool>(T::value), conjunction<Ts...>, T>::type
{};

template<typename ...> struct disjunction : std::false_type{};
template<typename T>   struct disjunction<T> : T {};
template<typename T, typename ... Ts>
struct disjunction<T, Ts...> :
    std::conditional<static_cast<bool>(T::value), T, disjunction<Ts...>>::type
{};

template<typename T>
struct negation : std::integral_constant<bool, !static_cast<bool>(T::value)>{};

// ---------------------------------------------------------------------------
// normal type checker

template<typename T> struct is_std_pair : std::false_type{};
template<typename T1, typename T2>
struct is_std_pair<std::pair<T1, T2>> : std::true_type{};

template<typename T> struct is_std_tuple : std::false_type{};
template<typename ... Ts>
struct is_std_tuple<std::tuple<Ts...>> : std::true_type{};

template<typename T> struct is_chrono_duration: std::false_type{};
template<typename Rep, typename Period>
struct is_chrono_duration<std::chrono::duration<Rep, Period>>: std::true_type{};

// ---------------------------------------------------------------------------
// C++14 index_sequence

template<std::size_t ... Ns> struct index_sequence{};

template<typename IS, std::size_t N> struct push_back_index_sequence{};
template<std::size_t N, std::size_t ... Ns>
struct push_back_index_sequence<index_sequence<Ns...>, N>
{
    typedef index_sequence<Ns..., N> type;
};

template<std::size_t N>
struct index_sequence_maker
{
    typedef typename push_back_index_sequence<
        typename index_sequence_maker<N-1>::type, N>::type type;
};
template<>
struct index_sequence_maker<0>
{
    typedef index_sequence<0> type;
};
template<std::size_t N>
using make_index_sequence = typename index_sequence_maker<N-1>::type;

// ---------------------------------------------------------------------------
// return_type_of_t

#if __cplusplus >= 201703L

template<typename F, typename ... Args>
using return_type_of_t = std::invoke_result_t<F, Args...>;

#else
// result_of is deprecated after C++17
template<typename F, typename ... Args>
using return_type_of_t = typename std::result_of<F(Args...)>::type;

#endif

// ---------------------------------------------------------------------------
// is_string_literal
//
// to use this, pass `typename remove_reference<T>::type` to T.

template<typename T>
struct is_string_literal:
disjunction<
    std::is_same<const char*, T>,
    conjunction<
        std::is_array<T>,
        std::is_same<const char, typename std::remove_extent<T>::type>
        >
    >{};

}// detail
}//toml
#endif // TOML_TRAITS