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This file is part of Logtalk https://logtalk.org/ SPDX-FileCopyrightText: 1998-2023 Paulo Moura <pmoura@logtalk.org> SPDX-License-Identifier: Apache-2.0

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http://www.apache.org/licenses/LICENSE-2.0

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A parametric object may be used to represent objects whose "state" is static and set when the object is defined. However, there can be only one parametric object with a given functor and arity. For example, if we define the following parametric object:

:- object(circle(_Radius, _Color)).
        ...
:- end_object.

then the following terms may be interpreted as references to the object above:

circle(1, blue)
circle(2, yellow)

In the context of parametric objects, the above terms are known as "parametric object proxies". Proxies represent different instantiations of a parametric object parameters. Proxy terms may be stored on the database as Prolog facts or as Prolog rules (parameter instantiation can be deduced instead of being fixed). This results in a very compact representation, which can be an advantage when dealing with a large number of objects with immutable state. In addition, all the predicates managing these compact representation are encapsulated in a parametric object. This can be, however, a fragile solution as changes on the parametric object ancestors may imply changes to the number and meaning of the parametric object parameters which, in turn, may imply changes to all the Prolog facts used to represent the individual objects.

Note that parametric objects can co-exist with "normal" objects. For example, when using a class-based design, we may use "normal" instances together with a parametric instance of the same class.