Help:Parameter default: Difference between revisions

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{{historical|reason=<br>Although some of it may still be relevant, this page describes techniques made obsolete by [[Help:ParserFunctions|ParserFunctions]] and [[Help:Lua|Lua]].|brief=y}}

'''Note:''' Information on this page relates to MediaWiki versions 1.6 and later.

Notation: on this page the wikitext <code>{{{A}}}</code> is written as {{mono|[{{var|a}}]}}.

In a [[help:template|template]], <code>[{{var|a}}|{{var|b}}]</code> is equal to {{mono|[{{var|a}}]}} if that is defined, and else equal to {{mono|{{var|b}}}}.

These results {{mono|[{{var|a}}]}} and {{mono|{{var|b}}}} can be end results, but they can also be parameter names, parameter values, template names, parts thereof, etc.

If the results are template names as part of template calls involving a parameter of the outer template which may be undefined, one can arrange that an inner template is called with a parameter depending on an undefined outer parameter only if the parameter concerned is not actually used in the inner template, e.g. dummy template {{Timc|x0}} can be called as <nowiki>{{tlx|x0|[a]}}</nowiki> even if {{mono|[{{var|a}}]}} is undefined, see e.g. {{Tim|foreach/pass1}}.

==Limitation==

In the case of multiple default parts, only the first applies: <code>[a|b|c|d]</code> is equivalent with <code>[a|b]</code>. The default part can only contain "<code>|"</code> as part of full template, parameter or link syntax within it, and within {{xtag|nowiki-tags}}. Note that "<code>|"</code> can be avoided in table syntax by applying HTML coding (element "<nowiki><{{tag|table></nowiki>"}}).

The expression for the parameter name can also contain "<code>|"</code>, as part of full template or parameter syntax within it.

Examples, using <code><nowiki>{{x3}}</nowiki></code> containing <syntaxhighlight lang="wikitext" inline>{{{1}}}{{{1}}}{{{1}}}</syntaxhighlight> and <syntaxhighlight lang="wikitext" inline>{{t2}}</syntaxhighlight> containing <syntaxhighlight lang="wikitext" inline>start-{{{1}}}-middle-{{{2}}}-end</syntaxhighlight>:

The expression for the parameter name can also contain "|", as part of full template or parameter syntax within it.

*<syntaxhighlight lang="wikitext" inline>{{{a|b|c|d}}}</syntaxhighlight> gives <code>{{{A|b|c|d}}}</code>

*<syntaxhighlight lang="wikitext" inline>{{{a|{{x3|b}}}}}</syntaxhighlight> gives <code>{{{A|bbb}}}</code>

*<kbd><nowikisyntaxhighlight lang="wikitext" inline>{{{a|{{{b|c}}}}}}</nowiki></kbdsyntaxhighlight> gives <kbdcode>{{{A|{{{b|c}}}}}}</kbdcode>

*<kbd><nowikisyntaxhighlight lang="wikitext" inline>{{{a|[[b|c]]}}}</nowiki></kbdsyntaxhighlight> gives <kbdcode>{{{A|[[b|c]]}}}</kbdcode>

*<kbd><nowikisyntaxhighlight lang="wikitext" inline>{{{{{x3|a}}|b}}}</nowiki></kbdsyntaxhighlight> gives <kbdcode>{{{{{x3|a}}aaa|b}}}</kbdcode> - parameter aaa is undefined

*<kbd><nowikisyntaxhighlight lang="wikitext" inline>{{{{{{a|b}}}|c}}}</nowiki></kbdsyntaxhighlight> gives <kbdcode>{{{{{{A|b}}}|c}}}</kbdcode> - parameter b is undefined

*<kbd><nowikisyntaxhighlight lang="wikitext" inline>{{{a|<nowiki>b|c</nowiki><nowiki><</nowiki>/nowiki>}}}</kbdsyntaxhighlight> gives <kbdcode>{{{A|<nowiki>b|c</nowiki>}}}</kbdcode> - works fine for rendering text, but is not suitable for putting parameters b and c in a template call (there is no function for removing nowiki tags):

Examples, using {{Timc|x3}}<br />and {{Timc|t2}}:

*:<kbd><nowikisyntaxhighlight lang="wikitext" inline>{{t2|{{{a|<nowiki>b|c|d}}}</nowiki>}}}}}</kbdsyntaxhighlight> gives <kbdcode>{{{A|start-b|c|d-middle-{{{2}}}-end</kbdcode>

*<kbd><nowiki>{{{a|{{x3|b}}}}}</nowiki></kbd> gives <kbd>{{{A|{{x3|b}}}}}</kbd>

*<kbd><nowiki>{{{a|{{{b|c}}}}}}</nowiki></kbd> gives <kbd>{{{A|{{{b|c}}}}}}</kbd>

*<kbd><nowiki>{{{a|[[b|c]]}}}</nowiki></kbd> gives <kbd>{{{A|[[b|c]]}}}</kbd>

*<kbd><nowiki>{{{{{x3|a}}|b}}}</nowiki></kbd> gives <kbd>{{{{{x3|a}}|b}}}</kbd> - parameter aaa is undefined

*<kbd><nowiki>{{{{{{a|b}}}|c}}}</nowiki></kbd> gives <kbd>{{{{{{A|b}}}|c}}}</kbd> - parameter b is undefined

*<syntaxhighlight lang="wikitext" inline>{{{a|b{{!}}c}}}</syntaxhighlight> gives <code>{{{a|b{{!}}c}}}</code>, and the bar will be interpreted by the next layer of templates.

*<kbd><nowiki>{{{a|<nowiki>b|c</nowiki><nowiki><</nowiki>/nowiki>}}}</kbd> gives <kbd>{{{A|<nowiki>b|c</nowiki>}}}</kbd> - works fine for rendering text, but is not suitable for putting parameters b and c in a template call (there is no function for removing nowiki tags):

*:<kbd><nowiki>{{t2|{{{a|<nowiki>b|c</nowiki><nowiki><</nowiki>/nowiki>}}}}}</kbd> gives <kbd>{{T2|{{{A|<nowiki>b|c</nowiki>}}}}}</kbd>

==Expressions containing a parameter, with default==

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For comparison using a="if" and c=d="", and also the shorter class name "if" instead of "HiddenStructure", the two lines are:

<syntaxhighlight lang="wikitext">

<nowiki><span class=" if{{{b|}}} "> ... </span></nowiki>

<nowiki>{{{ span class=" if{{{b|}}} | "> ... }}}</nowikispan>

{{{ if{{{b|}}} | ... }}}

</syntaxhighlight>

In the second method the wikitext in the template is 15 characters shorter for each optional item, but each call is 4 characters ("if=|") longer.

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{{Tim|fors}}, containing:

----

<presyntaxhighlight lang="wikitext">{{fors/aux

|v@=

|c={{{call}}}

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|pc4={{{pc4|=}}}|

1={{{1|@}}}|2={{{2|@}}}|3={{{3|@}}}

}}</presyntaxhighlight>

----
with {{Tim|fors/aux}}, containing:

----

<presyntaxhighlight lang="wikitext">{{{v{{{1}}}|{{{{{c}}}|{{{pc1}}}|{{{pc2}}}|{{{pc3}}}|{{{pc4}}}|{{{pv}}}={{{1}}}}}}}}

{{{v{{{2}}}|{{{s}}}{{{{{c}}}|{{{pc1}}}|{{{pc2}}}|{{{pc3}}}|{{{pc4}}}|{{{pv}}}={{{2}}}}}}}}

{{{v{{{3}}}|{{{s}}}{{{{{c}}}|{{{pc1}}}|{{{pc2}}}|{{{pc3}}}|{{{pc4}}}|{{{pv}}}={{{3}}}}}}}}</presyntaxhighlight>

----

In short form the latter consists of components

<codesyntaxhighlight lang="wikitext">[ v[''i''] | [s] {{[c]|[pc1]|[pc2]|[pc3]|[pc4]|[pv]=[''i'']}} ]</codesyntaxhighlight> (''i'' = 1, 2, 3, for ''i'' = 1 without [s])

or in terms of the parameters of the first template:

<codesyntaxhighlight lang="wikitext">[v[''i''|@] | [sep|] {{[call]|[pc1|]|[pc2|]|[pc3|]|[pc4|]|[pv|1]=[''i'']}} ]</codesyntaxhighlight>

This is indeed of the above-mentioned form <code>[a[b|c]|f([b])]</code>, with {{mono|1=a=v, b=''i'', c=@}}, and

<codesyntaxhighlight lang="wikitext">f(x) = [sep|] {{[call]|[pc1|]|[pc2|]|[pc3|]|[pc4|]|[pv|1]=x}}</codesyntaxhighlight>

The assumptions mentioned above apply for d equal to null, and provided that no [''i''] is equal to "@".

===Variations===

Since {{code|1=v@=null}} we can also take make the concatenation the outer operation:

<codesyntaxhighlight lang="wikitext">[v[''i''|@] | [sep|]] [v[''i''|@] | {{[call]|[pc1|]|[pc2|]|[pc3|]|[pc4|]|[pv|1]=[''i'']}} ]</codesyntaxhighlight>

==Conditional statement==

{{Tim|if}} contains:

----

<presyntaxhighlight lang="wikitext">{{{else{{{test|}}}|{{{test{{{test|}}}|{{{then|}}}}}}}}}</presyntaxhighlight>

----

or in short form:

<syntaxhighlight lang="text">[ else[test|] | [ test[test|] | [then|] ] ]</syntaxhighlight>

If [<code>{{bracket|test]}}</code> is defined this reduces to

<syntaxhighlight lang="text">[ else[test] | [ test[test] | [then|] ] ]</syntaxhighlight>

For test equal to null this reduces to [else<code>{{bracket|]else{{!}}}}</code>; otherwise, if no parameter name starting with "test" or "else" applies except these themselves, then this reduces to [then<code>{{bracket|]then{{!}}}}</code>.

If [<code>{{bracket|test]}}</code> is undefined we get

<syntaxhighlight lang="text">[ else | [then|] ]</syntaxhighlight>

==Last-but technique==

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</pre>

I.e., to replace "4", "3", "2", "1" with D₄, D₃, D₂, D₁. And D<i>_x</i>=[if[<i>x</i>|u]|<i>x-1</i>]. Like this, you can get "last but <i>x</i>" parameter value. <br>

Examples using <nowiki>{{Tim|lastbut0}} and {{Tim|lastbut1}}</nowiki>:

*<code><nowiki>{{lastbut0}}</nowiki></code> gives {{lastbut0}}no input.

*<code><nowiki>{{lastbut0|a}}</nowiki></code> gives {{lastbut0|a}}.

*<code><nowiki>{{lastbut0|a|b|c|d|e|f|g|h|i|j}}</nowiki></code> gives {{lastbut0|a|b|c|d|e|f|g|h|i|j}}.

*<code><nowiki>{{lastbut1|ifu=}}</nowiki></code> gives {{lastbut1|ifu=}}no input.

*<code><nowiki>{{lastbut1|ifu=|a}}</nowiki></code> gives {{lastbut1|ifu=|a}}no input.

*<code><nowiki>{{lastbut1|ifu=|a|b}}</nowiki></code> gives {{lastbut1|ifu=|a|b}}.

*<code><nowiki>{{lastbut1|ifu=|a|b|c|d|e|f|g|h|i|j}}</nowiki></code> gives {{lastbut1|ifu=|a|b|c|d|e|f|g|h|i|j}}.

*<code><nowiki>{{lastbut0|53=53|81=81|28=28}}</nowiki></code> gives {{lastbut0|53=53|81=81|28=28}} (finds maximum of a list of integers in the range 1 - 100)

See also {{TimcnlTim|max}}

==Server efficiency==

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==See also==

*{{Tim|T opt par}} - examples

==References==

{{Reflist}}