65 lines
1.3 KiB
Plaintext
65 lines
1.3 KiB
Plaintext
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/*
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These objects illustrate a variant of the "diamond problem" using
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a prototype hierarchy.
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In this simple case, a solution for making the overridden definition inherited
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by the bottom object the visible one is implemented using the alias/3 predicate
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directive.
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*/
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% root object, declaring and defining a predicate m/0:
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:- object(a2).
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:- public(m/0).
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m :-
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this(This),
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write('Default definition of method m/0 in object '),
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write(This), nl.
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:- end_object.
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% an object descending from the root object, which redefines predicate m/0:
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:- object(b2,
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extends(a2)).
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m :-
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this(This),
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write('Redefinition of method m/0 in object '),
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write(This), nl.
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:- end_object.
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% another object descending from the root object, which also redefines predicate m/0:
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:- object(c2,
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extends(a2)).
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m :-
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this(This),
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write('Redefinition of method m/0 in object '),
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write(This), nl.
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:- end_object.
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% bottom object, descending from the two previous objects and, as such, inheriting
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% two definitions for the predicate m/0; the overridden definition inherited from
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% object "c2" is renamed using the alias/3 directive and then we redefine the
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% predicate m/0 to call the renamed definition:
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:- object(d2,
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extends(b2, c2)).
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:- alias(c2, m/0, c2_m/0).
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m :-
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::c2_m.
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:- end_object.
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