std::experimental::optional<T>::operator=

1) If *this contains a value before the call, the contained value is destroyed by calling its destructor as if by val->T::~T(). *this

2,3) Assigns the state of other.

• If both *this and other
• If *this contains a value, but other does not, then the contained value is destroyed by calling its destructor. *this
• If other contains a value, then depending on whether *this contains a value, the contained value is either direct-initialized or assigned from *other (2) or std::move(*other) (3). Note that a moved-from optional still contains a value

4) Decay-only perfect-forwarded assignment: depending on whether *this contains a value before the call, the contained value is either direct-initialized from std::forward <U> (value) or assigned from std::forward <U> (value) . The function does not participate in overload resolution unless std::is_same < std::decay_t <U>, T> :: value is true

2-4) Throws any exception thrown by the constructor or assignment operator of T. If an exception is thrown, the initialization state of *this (and of other in case of (2)) is unchanged, i.e. if the object contained a value, it still contains a value, and the other way round. The contents of value and the contained values of *this and other depend on the exception safety guarantees of the operation from which the exception originates (copy-constructor, move-assignment, etc.).
(3) has the following noexcept declaration:

#include <experimental/optional>
#include <iostream>
 
int main()
{
    std::experimental::optional<const char*> s1 = "abc", s2; // constructor
    s2 = s1; // assignment
    s1 = "def"; // decaying assignment (U = char[4], T = const char*)
    std::cout << *s2 << ' ' << *s1 << '\n';
}

abc def