Return whether this function currently holds a target.
Declared in <bslstl_function.h>
explicit
operator bool() const noexcept;(C++11 and later) Return false if this object is empty, otherwise return true. Note that this is an explicit conversion operator and is typically invoked implicitly in contexts such as in the condition of an if or while statement, though it can also be invoked via an explicit cast.
true if this object holds a target, and false otherwise