Ayuda:Funciones de parser en plantillas

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<translate> When applying [[<tvar name=1>Special:MyLanguage/Help:Extension:ParserFunctions</tvar>|ParserFunctions]] to [[<tvar name=2>Special:MyLanguage/Help:Templates</tvar>|template]] parameters, a pipe symbol ("|") may be used to provide a default value, which is used when a parameter is not defined.</translate> <translate> Used in an #if parser function, the unexpanded text from the undefined parameter will evaluate as true, which may be an unexpected result.</translate>

<translate> Testing parameters with and without default values</translate>

<translate> Parameter</translate>		{{{1}}}, {{{param}}}	{{{1|}}}, {{{param|}}}	{{#if:<<translate> parameter</translate>>|True|False}}
<translate> Description</translate>	<translate> Example, unnamed and named</translate>			{{{1}}}, {{{param}}}	{{{1|}}}, {{{param|}}}
<translate> Undefined. More appropriate for use in named parameters.</translate>	{{template}}	{{{1}}}		True	False
<translate> Defined, but empty or null.</translate>	{{template|}}, {{template|1=}}, {{template|param=}}			False	False
<translate> Defined, non-empty, and non-null.</translate>	{{template|value}}, {{template|1=value}}, {{template|param=value}}	value	value	True	True

• {{{1}}}

<translate> Sample A</translate>

{{#if: {{{1}}} | <translate> Parameter 1 is not defined, or is defined and non-null/non-empty.</translate> | <translate> Parameter 1 is null. It contains only empty string(s) or breaking space(s) etc.</translate>}}

<translate> Result</translate>

<translate> Parameter 1 is not defined, or is defined and non-null/non-empty.</translate>

• {{{1|}}}

<translate> Sample B</translate>

{{#if: {{{1|}}} | <translate> Parameter 1 is defined and non-null/non-empty.</translate> | <translate> Parameter 1 is not defined, or is defined but null. It contains only empty string(s) or breaking space(s) etc.</translate>}}

<translate> Result</translate>

<translate> Parameter 1 is not defined, or is defined but null. It contains only empty string(s) or breaking space(s) etc.</translate>

<translate> The second usage (<tvar name=1>{{{1|}}}</tvar>, sample B) with present empty default is often the desired way to handle situations where a parameter exists, but is comprised only of empty space.

Testing and passing undefined parameters

</translate> <translate> To distinguish a possibly empty parameter from an unspecified one, compare it to itself using <tvar name=ifeq>{{#ifeq:}}</tvar> and different defaults.</translate> <translate> What the defaults are does not matter as long as they are different, so they are typically chosen to be short.</translate> <translate> The following all work equivalently:</translate>

{{#ifeq:{{{v|+}}}|{{{v|-}}}| <translate> v was defined (and may be empty)</translate> | <translate> v was not defined</translate> }}

{{#ifeq:{{{v|}}}|{{{v|-}}}| <translate> v was defined (and may be empty)</translate> | <translate> v was not defined</translate> }}

{{#ifeq:{{{v|}}}|{{{v}}}| <translate> v was defined (and may be empty)</translate> | <translate> v was not defined</translate> }}

<translate> In rare cases, a template behaves differently when a parameter is unspecified compared to when it is specified but empty. When this template is used by a wrapper template (which uses the same set of named parameters), one way to ensure undefined parameters remain undefined is as follows (the technique also works with numbered parameters): </translate>

{{wrapped_template|
normal_parameter={{{normal_parameter|}}}|
sensitive_parameter{{#if:{{{sensitive_parameter|}}}||NULL}}={{{sensitive_parameter}}}
}}

<translate> wrapped_template receives a defined normal_parameter in all cases. When normal_parameter is defined but empty and when it is undefined, wrapped_template receives an empty normal_parameter. </translate>

<translate> By contrast, the wrapped_template receives a defined sensitive_parameter only when it is indeed defined; when sensitive_parameter is undefined, the #if changes the parameter name to sensitive_parameterNULL.</translate> <translate> The suffixed parameter name must be meaningless to the wrapped_template for this to work properly.</translate>

<translate>

See also

</translate>

• Help:Extension:ParserFunctions
• Help:Templates

<translate>

• [[<tvar name=ext>Special:MyLanguage/Extension:Loops##forargs (experimental)</tvar>|Extension:Loops#forargs]]

</translate>