std::make_optional
Min standard notice:
Header: <optional>
- Creates an optional object from value. Effectively calls std::optional<std::decay_t
>(std::forward (value)).
# Declarations
template< class T >
constexpr std::optional<std::decay_t<T>> make_optional( T&& value );
(since C++17)
template< class T, class... Args >
constexpr std::optional<T> make_optional( Args&&... args );
(since C++17)
template< class T, class U, class... Args >
constexpr std::optional<T> make_optional( std::initializer_list<U> il,
Args&&... args );
(since C++17)
# Parameters
value: the value to construct optional object withil, args: arguments to be passed to the constructor of T
# Return value
The constructed optional object.
# Notes
T need not be movable for overloads (2,3) due to guaranteed copy elision.
# Example
#include <iomanip>
#include <iostream>
#include <optional>
#include <string>
#include <vector>
int main()
{
auto op1 = std::make_optional<std::vector<char>>({'a','b','c'});
std::cout << "op1: ";
for (char c : op1.value())
std::cout << c << ',';
auto op2 = std::make_optional<std::vector<int>>(5, 2);
std::cout << "\nop2: ";
for (int i : *op2)
std::cout << i << ',';
std::string str{"hello world"};
auto op3 = std::make_optional<std::string>(std::move(str));
std::cout << "\nop3: " << std::quoted(op3.value_or("empty value")) << '\n';
std::cout << "str: " << std::quoted(str) << '\n';
}