std::experimental::optional<T>:: optional

1) Constructs the object that does not contain a value .

2) Copy constructor: If other contains a value, initializes the contained value as if direct-initializing (but not direct-list-initializing) an object of type T with the expression * other . If other does not contain a value, constructs an object that does not contain a value .

3) Move constructor: If other contains a value, initializes the contained value as if direct-initializing (but not direct-list-initializing) an object of type T with the expression std :: move ( * other ) and does not make other empty: a moved-from optional still contains a value , but the value itself is moved from. If other does not contain a value, constructs an object that does not contain a value .

4) Constructs an optional object that contains a value , initialized as if direct-initializing (but not direct-list-initializing) an object of type T with the expression value . This constructor is constexpr if the constructor of T selected by direct-initialization is constexpr .

5) Constructs an optional object that contains a value , initialized as if direct-initializing (but not direct-list-initializing) an object of type T with the expression std :: move ( value ) . This constructor is constexpr if the constructor of T selected by direct-initialization is constexpr .

6) Constructs an optional object that contains a value , initialized as if direct-initializing (but not direct-list-initializing) an object of type T from the arguments std:: forward < Args > ( args ) ... .

7) Constructs an optional object that contains a value , initialized as if direct-initializing (but not direct-list-initializing) an object of type T from the arguments ilist, std:: forward < Args > ( args ) ... . The function does not participate in the overload resolution if std:: is_constructible < T, std:: initializer_list < U > & , Args && ... > :: value ! = true .

2) Throws any exception thrown by the constructor of T .

3) Throws any exception thrown by the constructor of T . Has the following noexcept declaration:

4-7) Throws any exception thrown by the constructor of T .

#include <experimental/optional>
#include <iostream>
#include <string>
 
int main()
{
    std::experimental::optional<int> o1,      // empty
                                     o2 = 1,  // init from rvalue
                                     o3 = o2; // copy-constructor
 
    std::experimental::optional<std::string> o4(std::experimental::in_place,
                                                {'a', 'b', 'c'});
 
    std::cout << *o2 << ' ' << *o3 << ' ' << *o4 << '\n';
}

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