62 lines
1.2 KiB
Plaintext
62 lines
1.2 KiB
Plaintext
|
/*
|
||
|
|
These metafile objects illustrate a variant of the "diamond problem" using
|
||
|
|
a prototype hierarchy.
|
||
|
|
|
||
|
|
In this simple case, a solution is presented for making two conflicting
|
||
|
|
definitions inherited by the bottom object visible through the use of the
|
||
|
|
alias/3 predicate directive.
|
||
|
|
*/
|
||
|
|
|
||
|
|
|
||
|
|
% root object, declaring and defining a predicate m/0:
|
||
|
|
|
||
|
|
:- object(a3).
|
||
|
|
|
||
|
|
:- public(m/0).
|
||
|
|
|
||
|
|
m :-
|
||
|
|
this(This),
|
||
|
|
write('Default definition of method m/0 in object '),
|
||
|
|
write(This), nl.
|
||
|
|
|
||
|
|
:- end_object.
|
||
|
|
|
||
|
|
|
||
|
|
% an object descending from the root object, which redefines predicate m/0:
|
||
|
|
|
||
|
|
:- object(b3,
|
||
|
|
extends(a3)).
|
||
|
|
|
||
|
|
m :-
|
||
|
|
this(This),
|
||
|
|
write('Redefinition of method m/0 in object '),
|
||
|
|
write(This), nl.
|
||
|
|
|
||
|
|
:- end_object.
|
||
|
|
|
||
|
|
|
||
|
|
% another object descending from the root object, which also redefines predicate m/0:
|
||
|
|
|
||
|
|
:- object(c3,
|
||
|
|
extends(a3)).
|
||
|
|
|
||
|
|
m :-
|
||
|
|
this(This),
|
||
|
|
write('Redefinition of method m/0 in object '),
|
||
|
|
write(This), nl.
|
||
|
|
|
||
|
|
:- end_object.
|
||
|
|
|
||
|
|
|
||
|
|
% bottom object, descending from the two previous objects and, as such, inheriting
|
||
|
|
% two definitions for the predicate m/0; both inherited definitions are renamed
|
||
|
|
% using the alias/3 directive:
|
||
|
|
|
||
|
|
:- object(d3,
|
||
|
|
extends(b3, c3)).
|
||
|
|
|
||
|
|
:- alias(b3, m/0, b3_m/0).
|
||
|
|
:- alias(c3, m/0, c3_m/0).
|
||
|
|
|
||
|
|
:- end_object.
|