Template:If empty
Uses Lua: |
- 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
editThe 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
editParameters used with {{if empty}} must be piped – i.e. include the ("Template:Thinsp|Template:Thinsp") as a trailing character – so that empty or undefined parameters aren't treated as text and returned incorrectly.
Exemples
editCode | Result | |
---|---|---|
{{if empty}} |
Returns an empty string. | |
{{if empty|one}} |
one | Returns the first parameter that is defined and not empty. |
{{if empty|one|two}} |
one | |
{{if empty|one|two|three|four}} |
one | |
{{if empty||two}} |
two | The first parameter is empty/undefined, so is passed over. |
{{if empty||two|three|four}} |
two | |
{{if empty||two||four}} |
two | |
{{if empty||||||||||ten}} |
ten | Unlike in previous versions, this template is no longer limited by 9 parameters. |
{{if empty|}} |
The only parameter is empty or undefined, so returns an empty string. | |
{{if empty||||}} |
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. |
The above documentation is transcluded from Template:If empty/doc (edit | history). Editors can experiment in this template's sandbox (create | mirror) and testcases (create) page. Please add categories to the /doc subpage. Subpages of this template. |