Kurt at 15:18, 20 July 2022

2022-07-20T15:18:41Z

← Older revision		Revision as of 10:18, 20 July 2022
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	{{Template redirect \|Ifempty \|First nonempty \|Use first nonempty \|Firstdata}}		{{Template redirect \|Ifempty \|First nonempty \|Use first nonempty \|Firstdata}}
	{{Lua\|Module:If empty}}		{{Lua\|Module:If empty}}
	~~{{High-use\|all-pages = yes}}~~

	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 <code><nowiki>{{if empty\|a\|b\|c}}</nowiki></code> instead of <code><nowiki>{{#if:a\|a\|{{#if:b\|b\|c}}}}</nowiki></code>, expression a and b do not have to be [[Don't repeat yourself\|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.		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 <code><nowiki>{{if empty\|a\|b\|c}}</nowiki></code> instead of <code><nowiki>{{#if:a\|a\|{{#if:b\|b\|c}}}}</nowiki></code>, expression a and b do not have to be [[Don't repeat yourself\|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.

Kurt: Created page with "{{Documentation subpage}} {{Template redirect |Ifempty |First nonempty |Use first nonempty |Firstdata}} {{Lua|Module:If empty}} {{High-use|all-pages = yes}} 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}} 2022-07-20T15:18:06Z Created page with "{{Documentation subpage}}  {{Template redirect |Ifempty |First nonempty |Use first nonempty |Firstdata}} {{Lua|Module:If empty}} {{High-use|all-pages = yes}} 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 <code><nowiki>{{if empty|a|b|c}}</nowiki></co..." New page {{Documentation subpage}}  {{Template redirect |Ifempty |First nonempty |Use first nonempty |Firstdata}} {{Lua|Module:If empty}} {{High-use|all-pages = yes}} 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 <code><nowiki>{{if empty|a|b|c}}</nowiki></code> instead of <code><nowiki>{{#if:a|a|{{#if:b|b|c}}}}</nowiki></code>, expression a and b do not have to be [[Don't repeat yourself|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: : <code><nowiki>{{If empty |{{{logo|}}} |{{{image|}}} |{{{picture|}}} |default.svg}}</nowiki></code> : <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". ===Rationale=== The MediaWiki parameter default function doesn't return the default value for empty parameters. That is, <code><nowiki>{{{logo|default.svg}}}</nowiki></code> does not return "default.svg" if the template was called like this: <code><nowiki>{{template|logo=}}</nowiki></code>. The usual workaround for a single parameter is: : <code><nowiki>{{#if:{{{logo|}}} |{{{logo}}} |default.svg}}</nowiki></code> : <nowiki>("If {{{logo}}} has a value, return it, else return "default.svg".")</nowiki> 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> : <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): : <code><nowiki>{{if empty |{{{logo|}}} |{{{image|}}} |{{{picture|}}} |default.svg}}</nowiki></code> ====Piping==== Parameters used with {{tlf|if empty}} must be [[Pipe (Unix)|pipe]]d – i.e. include the [[Vertical bar|vertical bar (pipe) symbol]] {{nowrap|("{{thin space}}|{{thin space}}")}} as a trailing character – so that empty or undefined parameters aren't treated as text and returned incorrectly. Hence, for example, <code><nowiki>{{{logo|}}}</nowiki></code>, <code><nowiki>{{{image|}}}</nowiki></code> and <code><nowiki>{{{picture|}}}</nowiki></code> rather than {{param|logo}}, {{param|image}} and {{param|picture}} in the above examples. ===Examples=== {{Aligned table |class=wikitable |cols=3 |col1style=padding-right:1.0em; |col2style=padding-left:0.5em;padding-right:1.0em; |col3style=padding-left:0.5em; |row1style=background:whitesmoke;padding-left:0.5em;font-weight:bold; | Code | Result | | {{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|two}} | {{if empty|one|two}} | | {{tlc|if empty|one|two|three|four}} | {{if empty|one|two|three|four}} | | {{tlc|if empty||two}} | {{if empty||two}} | The first parameter is empty/undefined, so is passed over. | {{tlc|if empty||two|three|four}} | {{if empty||two|three|four}} | | {{tlc|if empty||two||four}} | {{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. | {{tlc|if empty{{!}}}} | {{if empty|}} | The only parameter is empty or undefined, so 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}} | No pipe-characters following the names of the first two parameters ("1" and "2"), so the first of these 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}} | No pipe-character following the parameter name "logo", so the text "{{{logo}}}" 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. }} ===See also=== * {{tl|if all}} * {{tl|if either}} * [[Help:Parameter default]] * {{tl|Category see also if exists 2}} <includeonly>{{Sandbox other| |  [[Category:If-then-else templates]] [[Category:Parameter selection templates]] }}</includeonly>