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wikipeida>HTGS Clean up examples: Some were not displaying pipes properly because of {{tlc}}, other examples were unnecessary, others needed some explanatory text |
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<!----PLEASE ADD TEMPLATE CATEGORIES WHERE INDICATED AT THE BOTTOM OF THIS PAGE----> | <!----PLEASE ADD TEMPLATE CATEGORIES WHERE INDICATED AT THE BOTTOM OF THIS PAGE----> | ||
{{Cascade-protected template}} | {{Cascade-protected template}} | ||
{{ | {{used in system}} | ||
{{Lua|Module:If empty}} | {{Lua|Module:If empty}} | ||
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Typical usage is like this: | Typical usage is like this: | ||
: <code><nowiki>{{If empty |{{{logo|}}} |{{{image|}}} |{{{picture|}}} |default.svg}}</nowiki></code> | : <code><nowiki>{{If empty |{{{logo|}}} |{{{image|}}} |{{{picture|}}} |default.svg}}</nowiki></code> | ||
: <nowiki> | : — <nowiki>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".</nowiki> | ||
This returns the first of the parameters ''logo'', ''image'' and ''picture'' that is defined and non-empty, otherwise "default.svg". | This returns the first of the parameters ''logo'', ''image'' and ''picture'' that is defined and non-empty, otherwise "default.svg". | ||
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The usual workaround for a single parameter is: | The usual workaround for a single parameter is: | ||
: <code><nowiki>{{#if:{{{logo|}}} |{{{logo}}} |default.svg}}</nowiki></code> | : <code><nowiki>{{#if:{{{logo|}}} |{{{logo}}} |default.svg}}</nowiki></code> | ||
: <nowiki> | : — <nowiki>If {{{logo}}} has a value, return it, else return "default.svg".</nowiki> | ||
But this becomes complex when several parameters are to be checked: | But this becomes complex when several parameters are to be checked: | ||
: <code><nowiki>{{#if:{{{logo|}}} |{{{logo}}} |{{#if:{{{image|}}} |{{{image}}} |{{#if:{{{picture|}}} |{{{picture}}} |default.svg}} }} }}</nowiki></code> | : <code><nowiki>{{#if:{{{logo|}}} |{{{logo}}} |{{#if:{{{image|}}} |{{{image}}} |{{#if:{{{picture|}}} |{{{picture}}} |default.svg}} }} }}</nowiki></code> | ||
: <nowiki> | : — <nowiki>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".</nowiki> | ||
In these cases, {{tlf|if empty}} produces the simpler syntax (as above): | In these cases, {{tlf|if empty}} produces the simpler syntax (as above): | ||
: <code><nowiki>{{if empty |{{{logo|}}} |{{{image|}}} |{{{picture|}}} |default.svg}}</nowiki></code> | : <code><nowiki>{{if empty |{{{logo|}}} |{{{image|}}} |{{{picture|}}} |default.svg}}</nowiki></code> | ||
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| {{tlc|if empty}} | {{if empty}} | Returns an empty string. | | {{tlc|if empty}} | {{if empty}} | Returns an empty string. | ||
| {{tlc|if empty|one}} | {{if empty|one}} | Returns the first parameter that is defined and not empty. | | {{tlc|if empty|one}} | {{if empty|one}} | Returns the first parameter that is defined and not empty. | ||
| {{tlc|if empty|one|two|three|four}} | {{if empty|one|two|three|four}} | | | {{tlc|if empty|one|two|three|four}} | {{if empty|one|two|three|four}} | | ||
| {{ | | <code><nowiki>{{if empty||two}}</nowiki></code> | {{if empty||two}} | The first parameter is empty/undefined, so is passed over. | ||
| {{ | | <code><nowiki>{{if empty||two||four}}</nowiki></code> | {{if empty||two||four}} | | ||
| <code><nowiki>{{if empty||||||||||ten}}</nowiki></code> | {{if empty||||||||||ten}} | Unlike in previous versions, this template is no longer limited by 9 parameters. | | <code><nowiki>{{if empty||||||||||ten}}</nowiki></code> | {{if empty||||||||||ten}} | Unlike in previous versions, this template is no longer limited by 9 parameters. | ||
| {{tlc|if empty{{!}}}} | {{if empty|}} | The only parameter is empty or undefined, so returns an empty string. | | {{tlc|if empty{{!}}}} | {{if empty|}} | The only parameter is empty or undefined, so the template returns an empty string. | ||
| {{tlc|if empty|{{!}}{{!}}{{!}}{{!}}}} | {{if empty||||}} | Returns an empty string. | | {{tlc|if empty|{{!}}{{!}}{{!}}{{!}}}} | {{if empty||||}} | Returns an empty string. | ||
| <code><nowiki>{{if empty|{{{1|}}}|{{{2|}}}|three}}</nowiki></code> | {{if empty|{{{1|}}}|{{{2|}}}|three}} | | | <code><nowiki>{{if empty|{{{1|}}}|{{{2|}}}|three}}</nowiki></code> | {{if empty|{{{1|}}}|{{{2|}}}|three}} | Neither 1 nor 2 are defined, so "three" is returned. | ||
| <code><nowiki>{{if empty|{{{1}}}|{{{2}}}|three}}</nowiki></code> | {{if empty|{{{1}}}|{{{2}}}|three}} | No pipe-characters following the names of the first two parameters ("1" and "2"), so the first | | <code><nowiki>{{if empty|{{{1}}}|{{{2}}}|three}}</nowiki></code> | {{if empty|{{{1}}}|{{{2}}}|three}} | No pipe-characters following the names of the first two parameters ("1" and "2"), so the first is returned as text ("{{{1}}}"). | ||
| <code><nowiki>{{if empty|{{{logo|}}}|two}}</nowiki></code> | {{if empty|{{{logo|}}}|two}} | | | <code><nowiki>{{if empty|{{{logo|}}}|two}}</nowiki></code> | {{if empty|{{{logo|}}}|two}} | | ||
| <code><nowiki>{{if empty|{{{logo}}}|two}}</nowiki></code> | {{if empty|{{{logo}}}|two}} | No pipe-character following the parameter name "logo", so the text "{{{logo}}}" returned. | | <code><nowiki>{{if empty|{{{logo}}}|two}}</nowiki></code> | {{if empty|{{{logo}}}|two}} | No pipe-character following the parameter name "logo", so the text "{{{logo}}}" is returned. | ||
| <code><nowiki>{{if empty|p=q}}</nowiki></code> | {{if empty|p=q}} | The template identifies the parameters it receives as parameters 1 to 9, not using names such as "p", etc. | | <code><nowiki>{{if empty|p=q}}</nowiki></code> | {{if empty|p=q}} | The template identifies the parameters it receives as parameters 1 to 9, not using names such as "p", etc. | ||
}} | }} |
Revision as of 02:17, 17 August 2024
This is a documentation subpage for Template:If empty. It contains usage information, categories and other content that is not part of the original page. |
Template:Cascade-protected template Template:Used in system
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 (" | ") 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
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|three|four}} | one | |
{{if empty||two}} | two | The first parameter is empty/undefined, so is passed over. |
{{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 the template returns an empty string. | |
{{if empty|||||}} | Returns an empty string. | |
{{if empty|{{{1|}}}|{{{2|}}}|three}} | three | Neither 1 nor 2 are defined, so "three" is returned. |
{{if empty|{{{1}}}|{{{2}}}|three}} | {{{1}}} | No pipe-characters following the names of the first two parameters ("1" and "2"), so the first is 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}}}" is 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