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/*
* Copyright 2021 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 <ftl/details/concat.h>
namespace android::ftl {
// Lightweight (not allocating nor sprintf-based) concatenation.
//
// std::string_view name = "Volume";
// ftl::Concat string(ftl::truncated<3>(name), ": ", -3, " dB");
//
// assert(string.str() == "Vol: -3 dB");
// assert(string.c_str()[string.size()] == '\0');
//
template <std::size_t, typename... Ts>
struct Concat;
template <std::size_t N, typename T, typename... Ts>
struct Concat<N, T, Ts...> : Concat<N + details::StaticString<T>::N, Ts...> {
explicit constexpr Concat(T v, Ts... args) { append(v, args...); }
protected:
constexpr Concat() = default;
constexpr void append(T v, Ts... args) {
using Str = details::StaticString<T>;
const Str str(v);
// TODO: Replace with constexpr std::copy in C++20.
for (auto it = str.view.begin(); it != str.view.end();) {
*this->end_++ = *it++;
}
using Base = Concat<N + Str::N, Ts...>;
this->Base::append(args...);
}
};
template <std::size_t N>
struct Concat<N> {
static constexpr std::size_t max_size() { return N; }
constexpr std::size_t size() const { return end_ - buffer_; }
constexpr const char* c_str() const { return buffer_; }
constexpr std::string_view str() const {
// TODO: Replace with {buffer_, end_} in C++20.
return {buffer_, size()};
}
protected:
constexpr Concat() : end_(buffer_) {}
constexpr void append() { *end_ = '\0'; }
char buffer_[N + 1];
char* end_;
};
// Deduction guide.
template <typename... Ts>
Concat(Ts&&...) -> Concat<0, Ts...>;
template <std::size_t N>
constexpr auto truncated(std::string_view v) {
return details::Truncated<N>{v};
}
} // namespace android::ftl
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