polymorphism_under

'Under-the-hood' Polymorphism

Actually, _profile_engine() is not a function found in Mall::Instructor.
It's found in a package called Mall, from which Mall::Instructor -- and other subclasses such as Mall::Room and Mall::Schedule -- inherit.
Each Mall subclass displays its data in slightly different ways.
So each such subclass has its own _profile_subengine() to handle the messy details.
But each such _profile_subengine() has the same interface and similar internal structure.
The $self-> means: Call the version of _profile_subengine() found in the invoking package.