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// Copyright 2024 Huawei Cloud Computing Technology Co., Ltd.
//
// 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.
#ifndef INCLUDED_SRC_OTHER_TOOLS_TRANSFORMED_RANGE_HPP
#define INCLUDED_SRC_OTHER_TOOLS_TRANSFORMED_RANGE_HPP
#include <cstddef>
#include <functional>
#include <iterator>
#include <type_traits>
#include <utility> //std::move
#include "gsl/gsl"
// TODO(modernize): Replace any use of this class by C++20's
// std::ranges/std::views (clang version >= 16.0.0)
/// \brief Transform iterable sequence "on the fly" invoking the given
/// transformation callback. If the callback throws an exception,
/// std::terminate is called.
/// \tparam Iterator Type of the iterator of the sequence to be
/// transformed.
/// \tparam Result Type of the transformation result.
template <typename Iterator, typename Result>
class TransformedRange final {
public:
using converter_t =
std::function<Result(typename Iterator::value_type const&)>;
class iterator final {
public:
using value_type = std::remove_reference_t<Result>;
using pointer = value_type*;
using reference = value_type&;
using difference_type = std::ptrdiff_t;
using iterator_category = std::forward_iterator_tag;
iterator() noexcept = default;
iterator(Iterator iterator, converter_t c) noexcept
: iterator_(std::move(iterator)), c_(std::move(c)) {}
auto operator*() const noexcept -> decltype(auto) {
try {
return std::invoke(c_, *iterator_);
} catch (...) {
Ensures(false);
}
}
auto operator++() noexcept -> iterator& {
++iterator_;
return *this;
}
[[nodiscard]] friend auto operator==(iterator const& lhs,
iterator const& rhs) noexcept
-> bool {
return lhs.iterator_ == rhs.iterator_;
}
[[nodiscard]] friend auto operator!=(iterator const& lhs,
iterator const& rhs) noexcept
-> bool {
return not(lhs == rhs);
}
private:
Iterator iterator_{};
converter_t c_{};
};
TransformedRange(Iterator begin, Iterator end, converter_t c) noexcept
: begin_{std::move(begin), std::move(c)},
end_{std::move(end), nullptr} {}
[[nodiscard]] auto begin() const noexcept -> iterator { return begin_; }
[[nodiscard]] auto end() const noexcept -> iterator { return end_; }
private:
iterator const begin_;
iterator const end_;
};
// User-defined deduction guide to help compiler dealing with generic lambdas
// and invokable objects.
template <typename Iterator,
typename Function,
typename IteratorValue = typename Iterator::value_type>
TransformedRange(Iterator, Iterator, Function)
-> TransformedRange<Iterator,
std::invoke_result_t<Function, IteratorValue>>;
#endif // INCLUDED_SRC_OTHER_TOOLS_TRANSFORMED_RANGE_HPP
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