pair.hpp

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#pragma once
 
namespace flecs {
 
namespace _ {
    struct pair_base { };
} // namespace _
 
 
template <typename First, typename Second>
struct pair : _::pair_base {
    using type = conditional_t<!is_empty<First>::value || is_empty<Second>::value, First, Second>; 
    using first = First; 
    using second = Second; 
    pair(type& v) : ref_(v) { }
 
    pair(const type& v) : ref_(const_cast<type&>(v)) { }
 
    operator type&() {
        return ref_;
    }
 
    operator const type&() const {
        return ref_;
    }
 
    type* operator->() {
        return &ref_;
    }
 
    const type* operator->() const {
        return &ref_;
    }
 
    type& operator*() {
        return ref_;
    }
 
    const type& operator*() const {
        return ref_;
    }
 
private:
    type& ref_;
};
 
template <typename First, typename Second, if_t<is_empty<First>::value> = 0>
using pair_object = pair<First, Second>;
 
template <typename T>
using raw_type_t = remove_pointer_t<remove_reference_t<T>>;
 
template <typename T>
struct is_pair {
    static constexpr bool value = is_base_of_v<_::pair_base, raw_type_t<T>>;
};
 
template <typename T>
inline constexpr bool is_pair_v = is_pair<T>::value;
 
template <typename P>
using pair_first_t = transcribe_cv_t<remove_reference_t<P>, typename raw_type_t<P>::first>;
 
template <typename P>
using pair_second_t = transcribe_cv_t<remove_reference_t<P>, typename raw_type_t<P>::second>;
 
template <typename P>
using pair_type_t = transcribe_cvp_t<remove_reference_t<P>, typename raw_type_t<P>::type>;
 
template <typename T, typename U = int>
struct actual_type;
 
template <typename T>
struct actual_type<T, if_not_t< is_pair<T>::value >> {
    using type = T;
};
 
template <typename T>
struct actual_type<T, if_t< is_pair<T>::value >> {
    using type = pair_type_t<T>;
};
 
template <typename T>
using actual_type_t = typename actual_type<T>::type;
 
 
template<typename T>
struct base_type {
    using type = decay_t< actual_type_t<T> >;
};
 
template <typename T>
using base_type_t = typename base_type<T>::type;
 
 
template<typename T>
struct base_arg_type {
    using type = remove_pointer_t< remove_reference_t< actual_type_t<T> > >;
};
 
template <typename T>
using base_arg_type_t = typename base_arg_type<T>::type;
 
 
template <typename T>
struct is_actual {
    static constexpr bool value = is_same_v<T, actual_type_t<T>>;
};
 
template <typename T>
inline constexpr bool is_actual_v = is_actual<T>::value;
 
} // namespace flecs