Null object pattern: Difference between revisions

Revision as of 05:16, 1 July 2024

Revision as of 18:51, 7 August 2024

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Following the Smalltalk principle, ''everything is an object'', the absence of an object is itself modeled by an object, called <code>nil</code>. In the GNU Smalltalk for example, the class of <code>nil</code> is <code>UndefinedObject</code>, a direct descendant of <code>Object</code>.

Any operation that fails to return a sensible object for its purpose may return <code>nil</code> instead, thus avoiding the special case of returning "no object" unsupported by Smalltalk designers. This method has the advantage of simplicity (no need for a special case) over the classical "null" or "no object" or "null reference" approach. Especially useful messages to be used with <code>nil</code> are <code>isNil</code>, <code>ifNil:</code> or <code>ifNotNil:</code>,, which make it practical and safe to deal with possible references to <code>nil</code> in Smalltalk programs.

===Common Lisp===