std::future<T>::~future

~future();

(since C++11)

Releases any shared state. This means:

If the current object holds the last reference to its shared state, the shared state is destroyed.
The current object gives up its reference to its shared state.

These actions will not block for the shared state to become ready, except that they may block if all following conditions are satisfied:
- The shared state was created by a call to std::async.
- The shared state is not yet ready.
- The current object was the last reference to the shared state.

(since C++14)

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