Difference between revisions of "Template:If empty/doc"
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| − | <!----PLEASE ADD CATEGORIES WHERE INDICATED AT THE BOTTOM OF THIS PAGE----> | + | <!----PLEASE ADD TEMPLATE CATEGORIES WHERE INDICATED AT THE BOTTOM OF THIS PAGE----> |
| − | {{Template redirect |Ifempty |First nonempty |Use first nonempty}} | + | {{Template redirect |Ifempty |First nonempty |Use first nonempty |Firstdata}} |
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* {{tl|if all}} | * {{tl|if all}} | ||
* {{tl|if either}} | * {{tl|if either}} | ||
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* [[Help:Parameter default]] | * [[Help:Parameter default]] | ||
<includeonly>{{Sandbox other| | <includeonly>{{Sandbox other| | ||
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[[Category:If-then-else templates]] | [[Category:If-then-else templates]] | ||
[[Category:Parameter selection templates]] | [[Category:Parameter selection templates]] | ||
}}</includeonly> | }}</includeonly> | ||
Latest revision as of 13:51, 7 February 2021
| This is a documentation subpage for Template:If empty. It contains usage information, categories and other content that is not part of the original template page. |
| This template uses Lua: |
| This template is used on approximately 2,250,000 pages, or roughly 560% of all pages. To avoid major disruption and server load, any changes should be tested in the template's /sandbox or /testcases subpages, or in your own user subpage. The tested changes can be added to this page in a single edit. Consider discussing changes on the talk page before implementing them. Transclusion count updated automatically (see documentation). |
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. 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".
Contents
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 (" | ") 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 {{{logo}}}, {{{image}}} and {{{picture}}} in the above examples.
Examples
Script error: No such module "aligned table".
See also
- {{if all}}
- {{if either}}
- Help:Parameter default