std::any::has_value
| bool has_value() const noexcept; | (since C++17) | 
Checks whether the object contains a value.
Parameters
(none).
Return value
true if instance contains a value, otherwise false.
    © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
    http://en.cppreference.com/w/cpp/utility/any/has_value