Mal:If empty
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This is the {{If empty}} template.
- Update 2014 Dec 23: This template used to only take 9 parameters. This limit has been removed.
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".
Rationale
[rediger kilde]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
[rediger kilde]Parameters used with {{if empty}} must be piped – i.e. include the vertical bar (pipe) symbol ("Mal:Thinsp|Mal:Thinsp") 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 Mal:Param, Mal:Param and Mal:Param in the above examples.
Examples
[rediger kilde]| Code | Result | |
| i | Returns an empty string. | |
| i | one | Returns the first parameter that is defined and not empty. |
| i | one | |
| i | one | |
| i | two | The first parameter is empty/undefined, so is passed over. |
| i | two | |
| i | two | |
{{if empty||||||||||ten}} | ten | Unlike in previous versions, this template is no longer limited by 9 parameters. |
| i | The only parameter is empty or undefined, so returns an empty string. | |
| i | Returns an empty string. | |
{{if empty|{{{1|}}}|{{{2|}}}|three}} | three | |
{{if empty|{{{1}}}|{{{2}}}|three}} | {{{1}}} | No pipe-characters following the names of the first two parameters ("1" and "2"), so the first of these returned as text ("{{{1}}}"). |
{{if empty|{{{logo|}}}|two}} | two | |
{{if empty|{{{logo}}}|two}} | {{{logo}}} | No pipe-character following the parameter name "logo", so the text "{{{logo}}}" returned. |
{{if empty|p=q}} | The template identifies the parameters it receives as parameters 1 to 9, not using names such as "p", etc. |
See also
[rediger kilde]- {{if all}}
- {{if either}}
- Help:Parameter default