85 lines
2.3 KiB
C++
85 lines
2.3 KiB
C++
/*
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* Copyright 2021 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <ftl/details/concat.h>
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namespace android::ftl {
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// Lightweight (not allocating nor sprintf-based) concatenation.
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//
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// std::string_view name = "Volume";
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// ftl::Concat string(ftl::truncated<3>(name), ": ", -3, " dB");
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//
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// assert(string.str() == "Vol: -3 dB");
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// assert(string.c_str()[string.size()] == '\0');
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//
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template <std::size_t, typename... Ts>
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struct Concat;
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template <std::size_t N, typename T, typename... Ts>
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struct Concat<N, T, Ts...> : Concat<N + details::StaticString<T>::N, Ts...> {
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explicit constexpr Concat(T v, Ts... args) { append(v, args...); }
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protected:
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constexpr Concat() = default;
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constexpr void append(T v, Ts... args) {
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using Str = details::StaticString<T>;
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const Str str(v);
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// TODO: Replace with constexpr std::copy in C++20.
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for (auto it = str.view.begin(); it != str.view.end();) {
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*this->end_++ = *it++;
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}
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using Base = Concat<N + Str::N, Ts...>;
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this->Base::append(args...);
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}
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};
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template <std::size_t N>
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struct Concat<N> {
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static constexpr std::size_t max_size() { return N; }
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constexpr std::size_t size() const { return end_ - buffer_; }
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constexpr const char* c_str() const { return buffer_; }
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constexpr std::string_view str() const {
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// TODO: Replace with {buffer_, end_} in C++20.
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return {buffer_, size()};
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}
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protected:
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constexpr Concat() : end_(buffer_) {}
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constexpr void append() { *end_ = '\0'; }
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char buffer_[N + 1];
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char* end_;
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};
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// Deduction guide.
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template <typename... Ts>
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Concat(Ts&&...) -> Concat<0, Ts...>;
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template <std::size_t N>
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constexpr auto truncated(std::string_view v) {
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return details::Truncated<N>{v};
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}
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} // namespace android::ftl
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