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{{Lua|Module:If empty}} | {{Lua|Module:If empty}} | ||
This template is used inside other templates. It takes any number of parameters and returns the first found to be defined and non-empty. If none is found, nothing is returned. By writing <code><nowiki>{{if empty|a|b|c}}</nowiki></code> instead of <code><nowiki>{{#if:a|a|{{#if:b|b|c}}}}</nowiki></code>, expression a and b do not have to be | This template is used inside other templates. It takes any number of parameters and returns the first found to be defined and non-empty. If none is found, nothing is returned. By writing <code><nowiki>{{if empty|a|b|c}}</nowiki></code> instead of <code><nowiki>{{#if:a|a|{{#if:b|b|c}}}}</nowiki></code>, expression a and b do not have to be repeated and evaluated twice. The template provides a fallback order, similar to a try catch based "It is easier to ask for forgiveness than permission" (EAFP) programming style. | ||
Typical usage is like this: | Typical usage is like this: | ||
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====Piping==== | ====Piping==== | ||
Parameters used with {{tlf|if empty}} must be | Parameters used with {{tlf|if empty}} must be piped – i.e. include the vertical bar (pipe) symbol {{nowrap|("{{thin space}}|{{thin space}}")}} as a trailing character – so that empty or undefined parameters aren't treated as text and returned incorrectly. Hence, for example, <code><nowiki>{{{logo|}}}</nowiki></code>, <code><nowiki>{{{image|}}}</nowiki></code> and <code><nowiki>{{{picture|}}}</nowiki></code> rather than {{param|logo}}, {{param|image}} and {{param|picture}} in the above examples. | ||
===Examples=== | ===Examples=== | ||
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* {{tl|if all}} | * {{tl|if all}} | ||
* {{tl|if either}} | * {{tl|if either}} | ||
* | * Help:Parameter default | ||
* {{tl|Category see also if exists 2}} | * {{tl|Category see also if exists 2}} | ||
Revision as of 08:26, 8 April 2025
| This page uses Creative Commons Licensed content from Wikipedia (view authors). |
 | This is a documentation subpage for Template:If empty It may contain usage information, categories and other content that is not part of the original template page. |
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 | This template uses Lua: |
This template is used inside other templates. It takes any number of parameters and returns the first found to be defined and non-empty. If none is found, nothing is returned. By writing {{if empty|a|b|c}} instead of {{#if:a|a|{{#if:b|b|c}}}}, expression a and b do not have to be repeated and evaluated twice. The template provides a fallback order, similar to a try catch based "It is easier to ask for forgiveness than permission" (EAFP) programming style.
Typical usage is like this:
{{If empty |{{{logo|}}} |{{{image|}}} |{{{picture|}}} |default.svg}}- — Return {{{logo|}}} if it has a value; else {{{image|}}} if it has a value; else {{{picture|}}} if it has a value; else return "default.svg".
This returns the first of the parameters logo, image and picture that is defined and non-empty, otherwise "default.svg".
Rationale
The MediaWiki parameter default function doesn't return the default value for empty parameters. That is, {{{logo|default.svg}}} does not return "default.svg" if the template was called like this: {{template|logo=}}.
The usual workaround for a single parameter is:
{{#if:{{{logo|}}} |{{{logo}}} |default.svg}}- — If {{{logo}}} has a value, return it, else return "default.svg".
But this becomes complex when several parameters are to be checked:
{{#if:{{{logo|}}} |{{{logo}}} |{{#if:{{{image|}}} |{{{image}}} |{{#if:{{{picture|}}} |{{{picture}}} |default.svg}} }} }}- — If {{{logo}}} has a value, return it; else if {{{image}}} has a value, return that; else if {{{picture}}} has a value, return that; else return "default.svg".
In these cases, {{if empty}} produces the simpler syntax (as above):
{{if empty |{{{logo|}}} |{{{image|}}} |{{{picture|}}} |default.svg}}
Piping
Parameters used with {{if empty}} must be piped – i.e. include the vertical bar (pipe) symbol ("Template:Thin space|Template:Thin space") as a trailing character – so that empty or undefined parameters aren't treated as text and returned incorrectly. Hence, for example, {{{logo|}}}, {{{image|}}} and {{{picture|}}} rather than Template:Param, Template:Param and Template:Param in the above examples.
Examples
See also
- {{if all}}
- {{if either}}
- Help:Parameter default
- {{Category see also if exists 2}}