Template:if empty

The following documentation is located at Template:if empty/documentation. ^[edit]

Useful links: subpage list • links • redirects • transclusions • errors (parser/module) • sandbox

Uses 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}}}}, 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 {{{logo}}}, {{{image}}} and {{{picture}}} 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}}`	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}}`	Lua error.	The template identifies the parameters it receives as parameters 1 to 9, not using names such as "p", etc.

Rationale

Piping

Examples

See also