1// Copyright (c) 2019-present The Bitcoin Core developers
2// Distributed under the MIT software license, see the accompanying
3// file COPYING or http://www.opensource.org/licenses/mit-license.php.
4
5#ifndef BITCOIN_UTIL_VECTOR_H
6#define BITCOIN_UTIL_VECTOR_H
7
8#include <functional>
9#include <initializer_list>
10#include <optional>
11#include <type_traits>
12#include <utility>
13#include <vector>
14
15/** Construct a vector with the specified elements.
16 *
17 * This is preferable over the list initializing constructor of std::vector:
18 * - It automatically infers the element type from its arguments.
19 * - If any arguments are rvalue references, they will be moved into the vector
20 *   (list initialization always copies).
21 */
22template<typename... Args>
23inline std::vector<std::common_type_t<Args...>> Vector(Args&&... args)
24{
25    std::vector<std::common_type_t<Args...>> ret;
26    ret.reserve(sizeof...(args));
27    // The line below uses the trick from https://www.experts-exchange.com/articles/32502/None-recursive-variadic-templates-with-std-initializer-list.html
28    (void)std::initializer_list<int>{(ret.emplace_back(std::forward<Args>(args)), 0)...};
29    return ret;
30}
31
32/** Concatenate two vectors, moving elements. */
33template<typename V>
34inline V Cat(V v1, V&& v2)
35{
36    v1.reserve(v1.size() + v2.size());
37    for (auto& arg : v2) {
38        v1.push_back(std::move(arg));
39    }
40    return v1;
41}
42
43/** Concatenate two vectors. */
44template<typename V>
45inline V Cat(V v1, const V& v2)
46{
47    v1.reserve(v1.size() + v2.size());
48    for (const auto& arg : v2) {
49        v1.push_back(arg);
50    }
51    return v1;
52}
53
54/** Clear a vector (or std::deque) and release its allocated memory. */
55template<typename V>
56inline void ClearShrink(V& v) noexcept
57{
58    // There are various ways to clear a vector and release its memory:
59    //
60    // 1. V{}.swap(v)
61    // 2. v = V{}
62    // 3. v = {}; v.shrink_to_fit();
63    // 4. v.clear(); v.shrink_to_fit();
64    //
65    // (2) does not appear to release memory in glibc debug mode, even if v.shrink_to_fit()
66    // follows. (3) and (4) rely on std::vector::shrink_to_fit, which is only a non-binding
67    // request. Therefore, we use method (1).
68
69    V{}.swap(v);
70}
71
72template<typename V, typename L>
73inline std::optional<V> FindFirst(const std::vector<V>& vec, const L fnc)
74{
75    for (const auto& el : vec) {
76        if (fnc(el)) {
77            return el;
78        }
79    }
80    return std::nullopt;
81}
82
83#endif // BITCOIN_UTIL_VECTOR_H
84