Editing Modula-3 (section)

===Object-oriented===
Object-oriented programming techniques may be used in Modula-3, but their use is not a requirement. Many of the other features provided in Modula-3 (modules, generics) can usually take the place of object-orientation.

Object support is intentionally kept to its simplest terms. An object type (termed a "class" in other object-oriented languages) is introduced with the <code>OBJECT</code> declaration, which has essentially the same syntax as a <code>RECORD</code> declaration, although an object type is a reference type, whereas RECORDs in Modula-3 are not (similar to structs in C). Exported types are usually named T by convention, and create a separate "Public" type to expose the methods and data. For example:

<syntaxhighlight lang="modula2" highlight="1">
INTERFACE Person;

TYPE T <: Public;
  Public = OBJECT 
  METHODS
    getAge(): INTEGER;
    init(name: TEXT; age: INTEGER): T;
  END;

END Person.
</syntaxhighlight>
This defines an interface <code>Person</code> with two types, <code>T</code>, and <code>Public</code>, which is defined as an object with two methods, <code>getAge()</code> and <code>init()</code>. <code>T</code> is defined as a subtype of <code>Public</code> by the use of the <code><:</code> operator.

To create a new <code>Person.T</code> object, use the built in procedure <code>NEW</code> with the method <code>init()</code> as 
<syntaxhighlight lang="modula2">
VAR jim := NEW(Person.T).init("Jim", 25);
</syntaxhighlight>