1 // Copyright (c) 2019 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 <initializer_list>
9 #include <type_traits>
10 #include <vector>
11 
12 /** Construct a vector with the specified elements.
13  *
14  * This is preferable over the list initializing constructor of std::vector:
15  * - It automatically infers the element type from its arguments.
16  * - If any arguments are rvalue references, they will be moved into the vector
17  *   (list initialization always copies).
18  */
19 template<typename... Args>
Vector(Args &&...args)20 inline std::vector<typename std::common_type<Args...>::type> Vector(Args&&... args)
21 {
22     std::vector<typename std::common_type<Args...>::type> ret;
23     ret.reserve(sizeof...(args));
24     // The line below uses the trick from https://www.experts-exchange.com/articles/32502/None-recursive-variadic-templates-with-std-initializer-list.html
25     (void)std::initializer_list<int>{(ret.emplace_back(std::forward<Args>(args)), 0)...};
26     return ret;
27 }
28 
29 /** Concatenate two vectors, moving elements. */
30 template<typename V>
Cat(V v1,V && v2)31 inline V Cat(V v1, V&& v2)
32 {
33     v1.reserve(v1.size() + v2.size());
34     for (auto& arg : v2) {
35         v1.push_back(std::move(arg));
36     }
37     return v1;
38 }
39 
40 /** Concatenate two vectors. */
41 template<typename V>
Cat(V v1,const V & v2)42 inline V Cat(V v1, const V& v2)
43 {
44     v1.reserve(v1.size() + v2.size());
45     for (const auto& arg : v2) {
46         v1.push_back(arg);
47     }
48     return v1;
49 }
50 
51 #endif // BITCOIN_UTIL_VECTOR_H
52