mirror of https://github.com/bitcoin/bitcoin.git
84 lines
2.4 KiB
C++
84 lines
2.4 KiB
C++
// Copyright (c) 2019-2022 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#ifndef BITCOIN_UTIL_VECTOR_H
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#define BITCOIN_UTIL_VECTOR_H
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#include <functional>
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#include <initializer_list>
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#include <optional>
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#include <type_traits>
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#include <utility>
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#include <vector>
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/** Construct a vector with the specified elements.
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*
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* This is preferable over the list initializing constructor of std::vector:
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* - It automatically infers the element type from its arguments.
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* - If any arguments are rvalue references, they will be moved into the vector
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* (list initialization always copies).
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*/
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template<typename... Args>
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inline std::vector<typename std::common_type<Args...>::type> Vector(Args&&... args)
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{
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std::vector<typename std::common_type<Args...>::type> ret;
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ret.reserve(sizeof...(args));
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// The line below uses the trick from https://www.experts-exchange.com/articles/32502/None-recursive-variadic-templates-with-std-initializer-list.html
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(void)std::initializer_list<int>{(ret.emplace_back(std::forward<Args>(args)), 0)...};
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return ret;
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}
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/** Concatenate two vectors, moving elements. */
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template<typename V>
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inline V Cat(V v1, V&& v2)
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{
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v1.reserve(v1.size() + v2.size());
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for (auto& arg : v2) {
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v1.push_back(std::move(arg));
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}
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return v1;
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}
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/** Concatenate two vectors. */
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template<typename V>
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inline V Cat(V v1, const V& v2)
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{
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v1.reserve(v1.size() + v2.size());
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for (const auto& arg : v2) {
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v1.push_back(arg);
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}
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return v1;
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}
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/** Clear a vector (or std::deque) and release its allocated memory. */
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template<typename V>
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inline void ClearShrink(V& v) noexcept
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{
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// There are various ways to clear a vector and release its memory:
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//
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// 1. V{}.swap(v)
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// 2. v = V{}
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// 3. v = {}; v.shrink_to_fit();
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// 4. v.clear(); v.shrink_to_fit();
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//
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// (2) does not appear to release memory in glibc debug mode, even if v.shrink_to_fit()
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// follows. (3) and (4) rely on std::vector::shrink_to_fit, which is only a non-binding
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// request. Therefore, we use method (1).
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V{}.swap(v);
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}
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template<typename V, typename L>
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inline std::optional<V> FindFirst(const std::vector<V>& vec, const L fnc)
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{
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for (const auto& el : vec) {
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if (fnc(el)) {
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return el;
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}
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}
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return std::nullopt;
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}
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#endif // BITCOIN_UTIL_VECTOR_H
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