std::any::emplace
From cppreference.com
|
template
<
class ValueType, class... Args
>
std::decay_t <ValueType> & emplace( Args&&... args ) ; |
(1) | (since C++17) |
|
template
<
class ValueType, class U, class... Args
>
std::decay_t <ValueType> & emplace( std::initializer_list <U> il, Args&&... args ) ; |
(2) | (since C++17) |
Changes the contained object to one of type std::decay_t<ValueType>
First destroys the current contained object (if any) by reset(), then:
1) constructs an object of type std::decay_t<ValueType>, direct-non-list-initialized from
std::forward
<Args>
(args)
, as the contained object.
- This overload participates in overload resolution only if std::is_constructible_v < std::decay_t <ValueType>, Args...> and std::is_copy_constructible_v < std::decay_t <ValueType>> are both true
2) constructs an object of type std::decay_t<ValueType>, direct-non-list-initialized from
il, std::forward
<Args>
(args)
, as the contained object.
- This overload participates in overload resolution only if std::is_constructible_v < std::decay_t <ValueType>, std::initializer_list <U> &, Args...> and std::is_copy_constructible_v < std::decay_t <ValueType>> are both true
Template parameters
| ValueType | - | contained value type |
| Type requirements | ||
-
std::decay_t<ValueType> must meet the requirements of CopyConstructible
|
||
Return value
A reference to the new contained object.
Exceptions
Throws any exception thrown by T's constructor. If an exception is thrown, the previously contained object (if any) has been destroyed, and *this
Example
Run this code
#include <algorithm> #include <any> #include <iostream> #include <string> #include <vector> class Star { std::string name; int id; public: Star(std::string name, int id) : name{name}, id{id} { std::cout << "Star::Star(string, int)\n"; } void print() const { std::cout << "Star{\"" << name << "\" : " << id << "};\n"; } }; int main() { std::any celestial; // (1) emplace(Args&&... args); celestial.emplace<Star>("Procyon", 2943); const auto* star = std::any_cast<Star>(&celestial); star->print(); std::any av; // (2) emplace(std::initializer_list<U> il, Args&&... args); av.emplace<std::vector<char>>({'C', '+', '+', '1', '7'} /* no args */); std::cout << av.type().name() << '\n'; const auto* va = std::any_cast<std::vector<char>>(&av); std::for_each(va->cbegin(), va->cend(), [](char const& c) { std::cout << c; }); std::cout << '\n'; }
Possible output:
Star::Star(string, int)
Star{"Procyon" : 2943};
St6vectorIcSaIcEE
C++17See also
constructs an any object (public member function) |
|
| destroys contained object (public member function) |