You're trying to assign a type name (default_delete<T>) to a variable (m_onLeaveScope_empty), you forgot a ():
It worked in the case of the func argument because you never use the default value in your tests. As soon as you write something like scoped<int, decltype(f)> f23(23); you'll get the same error.
Anyway, it still won't work. Once you fix this you'll get another error: '`anonymous-namespace'::<lambda1>::(const `anonymous-namespace'::<lambda1> &)' : cannot convert parameter 1 from 'default_empty<T>' to 'const `anonymous-namespace'::<lambda1> &'
Again, you're mixing up things that look like functions but they have different types. In the particular case that triggered the above error your deleter is a lambda and the default_empty is a function object. They're not compatible.