Template:If empty/doc - Revision history

Matt at 22:11, 9 April 2025

2025-04-09T22:11:19Z

← Older revision		Revision as of 17:11, 9 April 2025
Line 3:		Line 3:
	<!----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}}

Matt at 15:03, 9 April 2025

2025-04-09T15:03:45Z

← Older revision		Revision as of 10:03, 9 April 2025
Line 27:		Line 27:

	====Piping====		====Piping====
	Parameters used with {{tlf\|if empty}} must be piped – i.e. include the 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 , and in the above examples.		Parameters used with {{tlf\|if empty}} must be piped – i.e. include the vertical bar (pipe) symbol {{nowrap\|("\|")}} 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 , and in the above examples.

	<includeonly>{{Sandbox other\|		<includeonly>{{Sandbox other\|

Matt at 09:00, 9 April 2025

2025-04-09T09:00:24Z

← Older revision		Revision as of 04:00, 9 April 2025
Line 27:		Line 27:

	====Piping====		====Piping====
	Parameters used with {{tlf\|if empty}} must be piped – i.e. include the 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.		Parameters used with {{tlf\|if empty}} must be piped – i.e. include the 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 , and in the above examples.

	<includeonly>{{Sandbox other\|		<includeonly>{{Sandbox other\|

Matt at 08:16, 9 April 2025

2025-04-09T08:16:48Z

@@ Line 28: / Line 28: @@
 ====Piping====
 Parameters used with {{tlf|if empty}} must be piped&nbsp;– i.e. include the vertical bar (pipe) symbol {{nowrap|("{{thin space}}&#124;{{thin space}}")}} as a trailing character&nbsp;– 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.
 <includeonly>{{Sandbox other|

Matt at 13:26, 8 April 2025

2025-04-08T13:26:33Z

← Older revision		Revision as of 08:26, 8 April 2025
Line 6:		Line 6:
	{{Lua\|Module:If empty}}		{{Lua\|Module:If empty}}

	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" (~~[[Time-of-check to time-of-use#Preventing TOCTOU\|~~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 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:		Typical usage is like this:
Line 27:		Line 27:

	====Piping====		====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.		Parameters used with {{tlf\|if empty}} must be piped – i.e. include the 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===		===Examples===
Line 52:		Line 52:
	* {{tl\|if all}}		* {{tl\|if all}}
	* {{tl\|if either}}		* {{tl\|if either}}
	* [[Help:Parameter default]]		* Help:Parameter default
	* {{tl\|Category see also if exists 2}}		* {{tl\|Category see also if exists 2}}

Matt at 21:10, 5 March 2025

2025-03-05T21:10:54Z

← Older revision		Revision as of 16:10, 5 March 2025
Line 1:		Line 1:
			{{wikipedia\|page name}}
	{{Documentation subpage}}		{{Documentation subpage}}
	<!----PLEASE ADD TEMPLATE CATEGORIES WHERE INDICATED AT THE BOTTOM OF THIS PAGE---->		<!----PLEASE ADD TEMPLATE CATEGORIES WHERE INDICATED AT THE BOTTOM OF THIS PAGE---->

Matt: Protected "Template:If empty/doc": Initial wiki setup ([Edit=Allow only administrators] (indefinite) [Move=Allow only administrators] (indefinite))

2025-03-05T19:57:40Z

Protected "Template:If empty/doc": Initial wiki setup ([Edit=Allow only administrators] (indefinite) [Move=Allow only administrators] (indefinite))

← Older revision	Revision as of 14:57, 5 March 2025
(No difference)

Matt: Created page with "{{Documentation subpage}} {{Cascade-protected template}} {{used in system}} {{Lua|Module:If empty}} 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}}}} 2025-03-05T18:54:36Z Created page with "{{Documentation subpage}}  {{Cascade-protected template}} {{used in system}} {{Lua|Module:If empty}} 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}}}}</n..." New page {{Documentation subpage}}  {{Cascade-protected template}} {{used in system}} {{Lua|Module:If empty}} 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" ([[Time-of-check to time-of-use#Preventing TOCTOU|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|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. | {{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. | <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 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}} | 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. }} ===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>