std::make_optional

Defined in header `<optional>`
template< class T > constexpr std::optional<std::decay_t<T>> make_optional( T&& value );	(1)	(since C++17)
template< class T, class... Args > constexpr std::optional<T> make_optional( Args&&... args );	(2)	(since C++17)
template< class T, class U, class... Args > constexpr std::optional<T> make_optional( std::initializer_list<U> il, Args&&... args );	(3)	(since C++17)

1) Creates an optional object from value. Effectively calls std::optional<std::decay_t<T>>(std::forward<T>(value))

2) Creates an optional object constructed in-place from args.... Equivalent to return std::optional<T>(std::in_place, std::forward<Args>(args)...);.

3) Creates an optional object constructed in-place from il and args.... Equivalent to return std::optional<T>(std::in_place, il, std::forward<Args>(args)...);.

Parameters

value	-	the value to construct optional object with
il, args	-	arguments to be passed to the constructor of `T`.

Return value

The constructed optional object.

Exceptions

Throws any exception thrown by the constructor of T.

Notes

T need not be movable for overloads (2-3) due to guaranteed copy elision.

Example

Run this code

#include <optional>
#include <iostream>
#include <iomanip>
#include <vector>
#include <string>
 
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: " << quoted(op3.value_or("empty value")) << '\n';
    std::cout << "str: " << std::quoted(str) << '\n';
}

Possible output:

op1: a,b,c,
op2: 2,2,2,2,2,
op3: "hello world"
str: ""

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Member functions
optional::optional (C++17)
optional::~optional (C++17)
optional::operator= (C++17)
Observers
optional::operator->optional::operator* (C++17)(C++17)
optional::operator booloptional::has_value (C++17)(C++17)
optional::value (C++17)
optional::value_or (C++17)
Monadic operations
optional::and_then (C++23)
optional::transform (C++23)
optional::or_else (C++23)
Modifiers
optional::emplace (C++17)
optional::swap (C++17)
optional::reset (C++17)
Non-member functions
operator==operator!=operator<operator<=operator>operator>=operator<=> (C++17)(C++17)(C++17)(C++17)(C++17)(C++17)(C++20)
make_optional (C++17)
swap (C++17)
Deduction guides
Helper classes
hash (C++17)
nullopt_t (C++17)
in_place_t (C++17)
bad_optional_access (C++17)
Helper objects
nullopt (C++17)
in_place (C++17)