1) Constructs the object thatdoes not contain a value.

2) Copy constructor: Ifother contains a value, initializes the contained value as ifdirect-initializing (but not direct-list-initializing) an object of typeT with the expression*other. Ifother does not contain a value, constructs an object thatdoes not contain a value.

3) Move constructor: Ifother contains a value, initializes the contained value as ifdirect-initializing (but not direct-list-initializing) an object of typeT with the expressionstd::move(*other) anddoes not makeother empty: a moved-from optional stillcontains a value, but the value itself is moved from. Ifother does not contain a value, constructs an object thatdoes not contain a value.

4) Constructs an optional object thatcontains a value, initialized as ifdirect-initializing (but not direct-list-initializing) an object of typeT with the expressionvalue. This constructor isconstexpr if the constructor ofT selected by direct-initialization isconstexpr.

5) Constructs an optional object thatcontains a value, initialized as ifdirect-initializing (but not direct-list-initializing) an object of typeT with the expressionstd::move(value). This constructor isconstexpr if the constructor ofT selected by direct-initialization isconstexpr.

6) Constructs an optional object thatcontains a value, initialized as ifdirect-initializing (but not direct-list-initializing) an object of typeT from the argumentsstd::forward<Args>(args)....

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

2) Throws any exception thrown by the constructor ofT.

3) Throws any exception thrown by the constructor ofT. Has the followingnoexcept declaration:

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

#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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