Types of reference

My thought on references in Object Orientated Programming.

A reference is free or fixed:

• I fixed reference can not be reassigned.
  e.g. reference in (C++), const pointer (C++), reference in functional language.
• A free reference can be reassigned.
  e.g. pointer in (C++), reference in (C#, Java, python …)

A reference is:

• not null-able: Can point to a valid object: e.g. Eiffel reference.
• union: Can point to a valid object, of one of a specified list of types.
• null-able: Can point to a valid object or null. e.g. Java, C#, python, Traditional Eiffel, Eiffel null-able reference.
• radical: Can point anywhere, can point to garbage or invalid memory e.g.  pointer, and even a reference in (C++).

 

A reference refers to something that is:

• Constant: all references in functional language.
• Mutable.