vector.h

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// Copyright (c) 2019 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
#ifndef BITCOIN_UTIL_VECTOR_H
#define BITCOIN_UTIL_VECTOR_H
 
#include <functional>
#include <initializer_list>
#include <optional>
#include <type_traits>
#include <vector>
 
template <typename... Args>
inline std::vector<typename std::common_type<Args...>::type>
Vector(Args &&...args) {
    std::vector<typename std::common_type<Args...>::type> ret;
    ret.reserve(sizeof...(args));
    // The line below uses the trick from
    // https://www.experts-exchange.com/articles/32502/None-recursive-variadic-templates-with-std-initializer-list.html
    (void)std::initializer_list<int>{
        (ret.emplace_back(std::forward<Args>(args)), 0)...};
    return ret;
}
 
template <typename V> inline V Cat(V v1, V &&v2) {
    v1.reserve(v1.size() + v2.size());
    for (auto &arg : v2) {
        v1.push_back(std::move(arg));
    }
    return v1;
}
 
template <typename V> inline V Cat(V v1, const V &v2) {
    v1.reserve(v1.size() + v2.size());
    for (const auto &arg : v2) {
        v1.push_back(arg);
    }
    return v1;
}
 
template <typename V> inline void ClearShrink(V &v) noexcept {
    // There are various ways to clear a vector and release its memory:
    //
    // 1. V{}.swap(v)
    // 2. v = V{}
    // 3. v = {}; v.shrink_to_fit();
    // 4. v.clear(); v.shrink_to_fit();
    //
    // (2) does not appear to release memory in glibc debug mode, even if
    // v.shrink_to_fit() follows. (3) and (4) rely on
    // std::vector::shrink_to_fit, which is only a non-binding request.
    // Therefore, we use method (1).
 
    V{}.swap(v);
}
 
template <typename V, typename L>
inline std::optional<V> FindFirst(const std::vector<V> &vec, const L fnc) {
    for (const auto &el : vec) {
        if (fnc(el)) {
            return el;
        }
    }
    return std::nullopt;
}
 
#endif // BITCOIN_UTIL_VECTOR_H