Editing Help/Templates (section)

=== Recursion in templates === <!--T:149-->
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<translate><!--T:124--> Including a template in itself won't throw MediaWiki into infinite recursion.</translate>
<translate><!--T:125--> MediaWiki will stop the recursion with the template's name in bold.</translate>
<translate><!--T:126--> For example, if the content of Template:Aaaa is <tvar name=code><code>a <nowiki></nowiki> z</code></tvar>, it'll display "<tvar name=result>a a <span class="error">Template loop detected:  '''Template:Aaaa'''</span> z z</tvar>".</translate>

<translate><!--T:219--> This safeguard precludes a potentially useful template idiom where a template self-normalizes its own calling arguments.</translate>
<translate><!--T:220--> In this forbidden example <tvar name=1><code>template:d</code></tvar> can either be called <tvar name=2><code><nowiki></nowiki></code></tvar> or <tvar name=3><code><nowiki></nowiki></code></tvar>.</translate>
<translate><!--T:221--> If called in the first manner, it recurses into itself with the second argument structure (obtained using string parser functions), which then follows a unified processing path.</translate>

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}|}|0|4}}|m=}|4|2}}|d=}|6|2}}}}|<!-- processing path with arguments y,m,d regardless of original call pattern -->}}
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<translate><!--T:222--> If <tvar name=1><code>template:d</code></tvar> is modified to recurse into <tvar name=2><code>template:d/2</code></tvar> and <tvar name=3><code>template:d/2</code></tvar> is an ''identical manual copy'' of <tvar name=4><code>template:d</code></tvar> this idiom works fine as the self-recursion safeguard operates dynamically and not statically.</translate>

<translate><!--T:223--> A feasible way for the MediaWiki software to loosen the self-recursion rule would be to require that each recursive call have a distinct argument count from all previous active calls, at most once recursing with the argument count non-decreasing.</translate>
<translate><!--T:224--> That would provide a strong guarantee against infinite self-recursion while enabling useful idioms such as the one described here in a flexible manner.</translate>

<translate><!--T:225--> If the processing path is of low complexity, a simple solution using only one template is to handle each calling convention on a separate if/else branch, duplicating the logic of the processing path within each case.</translate>
<translate><!--T:226--> If the processing path is more complex, each call-structure case can delegate to an implementation template with a unified call structure which provides the final template behaviour.</translate>

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