Maybe< T > 成员列表

成员的完整列表，这些成员属于 Maybe< T >,包括所有继承而来的类成员

is_absent() const	Maybe< T >
is_present() const	Maybe< T >
Just(const Q &value)	Maybe< T >	friend
Maybe(const Nothing &nothing)	Maybe< T >
Maybe(const Maybe< T > &other)	Maybe< T >
operator bool() const	Maybe< T >
value()	Maybe< T >
value_or(T &v)	Maybe< T >