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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
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]
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
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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
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| Code
| 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.
|
See also
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