if_and_only_if.hpp

 
#ifndef UFO_CONTAINER_TREE_PREDICATE_IF_AND_ONLY_IF_HPP
#define UFO_CONTAINER_TREE_PREDICATE_IF_AND_ONLY_IF_HPP
 
// UFO
#include <ufo/container/tree/predicate/filter.hpp>
#include <ufo/utility/type_traits.hpp>
 
// STL
#include <type_traits>
 
namespace ufo::pred
{
template <Filterable PredLeft, Filterable PredRight>
struct Iff {
    Iff(PredLeft const& left, PredRight const& right) noexcept : left(left), right(right) {}
 
    PredLeft  left;
    PredRight right;
};
 
template <Filterable PredLeft, Filterable PredRight>
struct Filter<Iff<PredLeft, PredRight>> {
    using Pred = Iff<PredLeft, PredRight>;
 
    template <class Tree>
    static constexpr void init(Pred& p, Tree const& t) noexcept
    {
        Filter<PredLeft>::init(p.left, t);
        Filter<PredRight>::init(p.right, t);
    }
 
    template <class Value>
    [[nodiscard]] static constexpr bool returnableValue(Pred const&  p,
                                                        Value const& v) noexcept
    {
        return Filter<PredLeft>::returnableValue(p.left, v) ==
               Filter<PredRight>::returnableValue(p.right, v);
    }
 
    template <class Tree>
    [[nodiscard]] static constexpr bool returnable(Pred const& p, Tree const& t,
                                                   typename Tree::Node const& n) noexcept
    {
        return Filter<PredLeft>::returnable(p.left, t, n) ==
               Filter<PredRight>::returnable(p.right, t, n);
    }
 
    template <class Tree>
    [[nodiscard]] static constexpr bool traversable(Pred const&, Tree const&,
                                                    typename Tree::Node const&) noexcept
    {
        // NOTE: This is not the same as the returnable check!
        return true;
    }
 
    template <class Tree>
    [[nodiscard]] static constexpr bool returnableRay(Pred const& p, Tree const& t,
                                                      typename Tree::Node const& n,
                                                      typename Tree::Ray const&  r) noexcept
    {
        return Filter<PredLeft>::returnableRay(p.left, t, n, r) ==
               Filter<PredRight>::returnableRay(p.right, t, n, r);
    }
 
    template <class Tree>
    [[nodiscard]] static constexpr bool traversableRay(Pred const&, Tree const&,
                                                       typename Tree::Node const&,
                                                       typename Tree::Ray const&) noexcept
    {
        // NOTE: This is not the same as the returnable check!
        return true;
    }
};
 
namespace detail
{
template <Filterable T, Filterable L, Filterable R>
struct contains_pred<T, Iff<L, R>>
    : std::disjunction<contains_pred<T, L>, contains_pred<T, R>> {
};
 
template <Filterable T, Filterable L, Filterable R>
struct contains_always_pred<T, Iff<L, R>> : std::false_type {
};
}  // namespace detail
}  // namespace ufo::pred
 
#endif  // UFO_CONTAINER_TREE_PREDICATE_IF_AND_ONLY_IF_HPP