Message Passing differs from a simple function in a number of very
important respects:
-
When a message is passed, it is always transmitted to a
specific instance. This instance is called the receiver.
-
The class of the receiver will decide the particular method that is invoked.
-
When the method is invoked, the receiver is passed as an implicit extra
parameter.
(Accessible using a pseudo-variable, named self in Smalltalk and
Object Pascal, named this in C++ and Java)