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people

This example illustrates how to define object constructors for a simple hierarchy of objects representing persons, students, and teachers. For simplicity, prototypes are used instead of classes. Logtalk provides a low-level, built-in predicate, create_object/4, for dynamically creating new objects. This predicate can be used to define object constructors, similar to those used in other OOP languages.

This example also illustrates how to efficiently represent objects with immutable state using parametric objects and object proxies (Prolog facts; see also the proxies example). This alternative is often a good choice when dealing with a very large number of objects due to its compact representation and/or connecting Prolog data tables with a Logtalk object hierarchies.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

%versions

Load the example:

logtalk_load(people(loader)).

Create two new persons:

person::new(Id1, 'Oscar the Grouch', '1969/11/10'), person::new(Id2, 'Cookie Monster', '1969/12/02').

Print a description of a person:

o2::print.

Create a new teacher and a new student:

teacher::new(Id3, 'Gordon Robinson', '1969/11/10', '3.2'), student::new(Id4, 'Roosevelt Franklin', '1969/11/10', 'Blue').

<!-- Id3 = o3, Id4 = o4.

Print a description of a student:

o4::print.

Try the alternative object representations using the object proxies:

{student('Roosevelt Franklin', _, _)}::print.