include/ftl/array_traits.h

/*
 * Copyright 2020 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#pragma once

#include <algorithm>
#include <iterator>
#include <new>
#include <type_traits>

#define FTL_ARRAY_TRAIT(T, U) using U = typename ArrayTraits<T>::U

namespace android::ftl {

template <typename T>
struct ArrayTraits {
    using value_type = T;
    using size_type = std::size_t;
    using difference_type = std::ptrdiff_t;

    using pointer = value_type*;
    using reference = value_type&;
    using iterator = pointer;
    using reverse_iterator = std::reverse_iterator<iterator>;

    using const_pointer = const value_type*;
    using const_reference = const value_type&;
    using const_iterator = const_pointer;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;

    template <typename... Args>
    static pointer construct_at(const_iterator it, Args&&... args) {
        void* const ptr = const_cast<void*>(static_cast<const void*>(it));
        if constexpr (std::is_constructible_v<value_type, Args...>) {
            // TODO: Replace with std::construct_at in C++20.
            return new (ptr) value_type(std::forward<Args>(args)...);
        } else {
            // Fall back to list initialization.
            return new (ptr) value_type{std::forward<Args>(args)...};
        }
    }
};

// CRTP mixin to define iterator functions in terms of non-const Self::begin and Self::end.
template <typename Self, typename T>
class ArrayIterators {
    FTL_ARRAY_TRAIT(T, size_type);

    FTL_ARRAY_TRAIT(T, reference);
    FTL_ARRAY_TRAIT(T, iterator);
    FTL_ARRAY_TRAIT(T, reverse_iterator);

    FTL_ARRAY_TRAIT(T, const_reference);
    FTL_ARRAY_TRAIT(T, const_iterator);
    FTL_ARRAY_TRAIT(T, const_reverse_iterator);

    Self& self() const { return *const_cast<Self*>(static_cast<const Self*>(this)); }

public:
    const_iterator begin() const { return cbegin(); }
    const_iterator cbegin() const { return self().begin(); }

    const_iterator end() const { return cend(); }
    const_iterator cend() const { return self().end(); }

    reverse_iterator rbegin() { return std::make_reverse_iterator(self().end()); }
    const_reverse_iterator rbegin() const { return crbegin(); }
    const_reverse_iterator crbegin() const { return self().rbegin(); }

    reverse_iterator rend() { return std::make_reverse_iterator(self().begin()); }
    const_reverse_iterator rend() const { return crend(); }
    const_reverse_iterator crend() const { return self().rend(); }

    iterator last() { return self().end() - 1; }
    const_iterator last() const { return self().last(); }

    reference front() { return *self().begin(); }
    const_reference front() const { return self().front(); }

    reference back() { return *last(); }
    const_reference back() const { return self().back(); }

    reference operator[](size_type i) { return *(self().begin() + i); }
    const_reference operator[](size_type i) const { return self()[i]; }
};

// Mixin to define comparison operators for an array-like template.
// TODO: Replace with operator<=> in C++20.
template <template <typename, std::size_t> class Array>
struct ArrayComparators {
    template <typename T, std::size_t N, std::size_t M>
    friend bool operator==(const Array<T, N>& lhs, const Array<T, M>& rhs) {
        return lhs.size() == rhs.size() && std::equal(lhs.begin(), lhs.end(), rhs.begin());
    }

    template <typename T, std::size_t N, std::size_t M>
    friend bool operator<(const Array<T, N>& lhs, const Array<T, M>& rhs) {
        return std::lexicographical_compare(lhs.begin(), lhs.end(), rhs.begin(), rhs.end());
    }

    template <typename T, std::size_t N, std::size_t M>
    friend bool operator>(const Array<T, N>& lhs, const Array<T, M>& rhs) {
        return rhs < lhs;
    }

    template <typename T, std::size_t N, std::size_t M>
    friend bool operator!=(const Array<T, N>& lhs, const Array<T, M>& rhs) {
        return !(lhs == rhs);
    }

    template <typename T, std::size_t N, std::size_t M>
    friend bool operator>=(const Array<T, N>& lhs, const Array<T, M>& rhs) {
        return !(lhs < rhs);
    }

    template <typename T, std::size_t N, std::size_t M>
    friend bool operator<=(const Array<T, N>& lhs, const Array<T, M>& rhs) {
        return !(lhs > rhs);
    }
};

} // namespace android::ftl