std::future::operator=

From cppreference.com
future& operator=( future&& other );
(1) (since C++11)
future& operator=( const future& other ) = delete;
(2) (since C++11)

Assigns the contents of another future object.

1) Releases any shared state and move-assigns the contents of other to *this. After the assignment, other.valid() == false and this->valid() will yield the same value as other.valid() before the assignment.

2) std::future is not CopyAssignable.

[edit] Parameters

other - a std::future that will transfer state to *this

[edit] Return value

*this

[edit] Exceptions

noexcept specification:  
noexcept
  (since C++11)