stabl@unipas.fmi.uni-passau.de (Robert Stabl) (07/11/89)
Hello,
I have a question about the Eiffel class "SORTED_LIST".
The definition of SORTED_LIST starts with the following line:
class SORTED_LIST [ T -> COMPARABLE ] export ....
What does the '->' stand for?
What is the semantic of this (polymorphic) class definition?
Greetings
Robert.
--
\ Robert Stabl =|= stabl@unipas.fmi.uni-passau.de /
\ Dept. of Computer Science |=| stabl%unipas.fmi.uni-passau.de@unido.BITNET /
/ University of Passau =|= stabl%unipas.fmi.uni-passau.de@relay.CS.NET \
/ West Germany |=| Phone: +49 851/509-346 \bertrand@eiffel.UUCP (Bertrand Meyer) (07/14/89)
From <610@unipas.fmi.uni-passau.de> by stabl@unipas.fmi.uni-passau.de (Robert Stabl): > I have a question about the Eiffel [basic library] class "SORTED_LIST". > > The definition of SORTED_LIST starts with the following line: > class SORTED_LIST [ T -> COMPARABLE ] export .... > > What does the '->' stand for? Since no one else seems to have answered let me explain. This is ``constrained genericity'', which means that any actual generic parameter used for the formal T generic parameter should be a descendant of class COMPARABLE, that is to say equipped with operations <=, <, > etc. For some reason that I don't recall (probably just time constraints) this important facility did not find its way into the book ``Object-Oriented Software Construction'' - more precisely, chapter 19, ``Genericity versus Inheritance'', where it belongs. The only glimpse of it is exercise 19.5, where it is discussed in the conditional (``Consider the usefulness of an extension...''). Constrained genericity is described in the 2.1 Eiffel User's Manual, as well as in the new Eiffel Reference Manual distributed with 2.2. -- Bertrand Meyer bertrand@eiffel.com