Singleton: Difference between revisions

=={{header|Logtalk}}==

Logtalk supports both classes and prototypes. A prototype is a much simpler solution for defining a singleton object than defining a class with only an instance.

<lang logtalk>

:- object(singleton).

:- public(value/1).

value(Value) :-

state(Value).

:- public(set_value/1).

set_value(Value) :-

retract(state(_)),

assertz(state(Value)).

:- private(state/1).

:- dynamic(state/1).

state(0).

:- end_object.

</lang>

A simple usage example after compiling and loading the code above:

<lang logtalk>

| ?- singleton::value(Value).

Value = 0

yes

| ?- singleton::(set_value(1), value(Value)).

Value = 1

yes

</lang>