vector_view.hpp

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// Man Group Operations Limited
//
// 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 <ranges>
#include <vector>
 
#if defined(__cpp_lib_format)
#    include <format>
#endif
 
namespace sparrow
{
    template <class T>
    class vector_view : public std::span<T>
    {
    public:
 
        using base_type = std::span<T>;
        using value_type = typename base_type::value_type;
 
        using base_type::base_type;
 
        explicit operator std::vector<value_type>() const noexcept
        {
            return std::vector<value_type>(this->begin(), this->end());
        }
    };
 
    template <class T>
    constexpr bool operator==(const vector_view<T>& lhs, const vector_view<T>& rhs)
    {
        return std::ranges::equal(lhs, rhs);
    }
 
    template <class T>
    constexpr bool operator==(const vector_view<T>& lhs, const std::vector<std::decay_t<T>>& rhs)
    {
        return std::ranges::equal(lhs, rhs);
    }
 
    template <class T>
    constexpr std::compare_three_way_result<T> operator<=>(const vector_view<T>& lhs, const vector_view<T>& rhs)
    {
        return std::lexicographical_compare_three_way(lhs.begin(), lhs.end(), rhs.begin(), rhs.end());
    }
 
    template <class T>
    constexpr std::compare_three_way_result<T>
    operator<=>(const vector_view<T>& lhs, const std::vector<std::decay_t<T>>& rhs)
    {
        return std::lexicographical_compare_three_way(lhs.begin(), lhs.end(), rhs.begin(), rhs.end());
    }
}
 
#if defined(__cpp_lib_format)
template <class T>
struct std::formatter<sparrow::vector_view<T>>
{
    constexpr auto parse(std::format_parse_context& ctx)
    {
        return ctx.begin();  // Simple implementation
    }
 
    auto format(const sparrow::vector_view<T>& vec, std::format_context& ctx) const
    {
        std::format_to(ctx.out(), "<");
        if (!vec.empty())
        {
            for (std::size_t i = 0; i < vec.size() - 1; ++i)
            {
                std::format_to(ctx.out(), "{}, ", vec[i]);
            }
        }
        return std::format_to(ctx.out(), "{}>", vec.back());
    }
};
 
template <typename T>
std::ostream& operator<<(std::ostream& os, const sparrow::vector_view<T>& value)
{
    os << std::format("{}", value);
    return os;
}
 
#endif