Difference between revisions of "Help:Parser functions in templates"

Latest revision as of 23:42, 31 October 2013

When applying ParserFunctions to template parameters, a pipe symbol ("|") may be used to provide the empty string as default value, in order to indicate how to handle things if a parameter is or is not passed in.

{{{1}}}

Sample A: {{#if: {{{1}}} | Parameter 1 is not defined, or is defined and non-null/non-empty. | Parameter 1 is null. It contains only empty string(s) or breaking space(s) etc.}}

Result: {{#if: {{{1}}} | Parameter 1 is not defined, or is defined and non-null/non-empty. | Parameter 1 is null. It contains only empty string(s) or breaking space(s) etc.}}

{{{1|}}}

Sample B: {{#if: {{{1|}}} | Parameter 1 is defined and non-null/non-empty. | Parameter 1 is not defined, or is defined but null. It contains only empty string(s) or breaking space(s) etc.}}

Result: {{#if: | Parameter 1 is defined and non-null/non-empty. | Parameter 1 is not defined, or is defined but null. It contains only empty string(s) or breaking space(s) etc.}}

Comparison

Example of usage in a template unnamed first parameter (1=) named parameter (param=)	Condition of parameter	Sample A: {{#if: {{{1}}}\| true\| false}} {{#if: {{{param}}}\| true\| false}}	Sample B: {{#if: {{{1\|}}}\| true\| false}} {{#if: {{{param\|}}}\| true\| false}}
`{{template}}`	not defined: parameter not used, important for named parameters	TRUE	FALSE
`{{template\|}} .. {{template\|1=}} .. {{template\|param=}}`	defined, but null/empty	FALSE	FALSE
`{{template\|value}} .. {{template\|1=value}} .. {{template\|param=value}}`	defined and NOT null neither empty	TRUE	TRUE

The second usage ({{{1|}}}, sample B) with present empty default is often the desired way to handle situations where a parameter exists, but is comprised only of empty space.

One way to test whether a parameter was specified in a template call is thus: {{#ifeq:{{{v|}}}|{{{v|-}}}| v was specified (and may be empty) | v was not specified }}

In rare cases, a template behaves differently when a parameter is unspecified compared to when it is specified but empty. When this template is used by a wrapper template (which uses the same set of named parameters), one way to ensure undefined parameters remain undefined is as follows (the technique also works with numbered parameters):

<!-- wrapper template code -->
{{wrapped_template|
normal_parameter={{{normal_parameter|}}}|
sensitive_parameter{{#if:{{{sensitive_parameter|}}}||NULL}}={{{sensitive_parameter}}}|
...
}}

Note that the wrapped_template receives a specified but empty normal_parameter in two cases: when normal_parameter is specified and empty, and when normal_parameter is unspecified (because the default empty value is then specified by the wrapper template).

By contrast, the wrapped_template receives a specified sensitive_parameter only when it is indeed specified, because the #if changes the wrapped_template parameter name to « sensitive_parameterNULL » when sensitive_parameter is undefined. Note also that wrapped_template receives a specified and empty sensitive_parameter only when the wrapper template receives a specified and empty sensitive_parameter. Of course, one must make sure the suffixed wrapped_template parameter name is meaningless to the wrapped_template for this to work properly.

Difference between revisions of "Help:Parser functions in templates"

Latest revision as of 23:42, 31 October 2013

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Revision as of 18:13, 21 April 2012 (view source) Technical 13 (talk) (Made the comparison table MUCH less confusing.)	Latest revision as of 23:42, 31 October 2013 (view source) Silvia (talk \| contribs) m (1 revision)
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