Template:If/doc: Difference between revisions

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With this template the [[Help:parser function|parser functions]] with names starting with "#if" can be used in a way such that they do not [[m:Help:Newlines_and_spaces#Trimming_on_expansion|strip spaces and newlines]] from the "then" and "else" part. Spaces still do not affect the outcome of the condition. Parameter 1 selects the if-type as "eq", "expr", "exist" or "error" (for #iferror), or empty "||" for a simple if-there (for #if). The template can be repeatedly nested 6 or 7 levels, one inside the other, because the outer-most is completed before running either the then/else inner levels.

*<nowiki>{{if||x| p | q }}</nowiki> gives "{{if||x| p | q }}". Notice the ''pair'' of vertical bars surrounding the empty first parameter.

*<nowiki>{{if|expr|2<3| p | q }}</nowiki> gives " p "

*<nowiki>{{if|eq| u |u| p | q }}</nowiki> gives "{{if|eq| u |u| p | q }}"

*<nowiki>{{if|exist| Help:Link | p | q }}</nowiki> gives "{{if|exist| Help:Link | p | q }}"

*<nowiki>{{if|error|{{#expr:x}}| p | q }}</nowiki> gives "{{if|error|{{#expr:x}}| p | q }}"

*<nowiki>{{#if:x| p | q }}</nowiki> gives "{{#if:x| p | q }}"

*<nowiki>{{#ifexpr:2<3| p | q }}</nowiki> gives "{{#ifexpr:2<3| p | q }}"

*<nowiki>{{#ifeq: u |u| p | q }}</nowiki> gives "{{#ifeq: u |u| p | q }}"

*<nowiki>{{#ifexist: Help:Link | p | q }}</nowiki> gives "{{#ifexist: Help:Link | p | q }}"

*<nowiki>{{#iferror:{{#expr:x}}| p | q }}</nowiki> gives "{{#iferror:{{#expr:x}}| p | q }}"

For example, with a template named ''Template:Template name'' containing the code <nowiki>{{#ifeq: {{{parameter}}} |u| p | q }}</nowiki>, entering the code <nowiki>{{{Template name|parameter=u}}}</nowiki> into an article gives "p", but <nowiki>{{{Template name|parameter=v}}}</nowiki> gives "q".

'''Indentation:''' If indenting the markup, care must be taken to avoid extra newlines when indenting "}}" on the next line. An extra bar pipe "|" can be added after the else-clause to complete that text, and allow "}}" to then be placed anywhere without adding a newline into the else-clause. For example:

:::* <nowiki>{{if|{{{1|}}}</nowiki><br>&nbsp; &nbsp; |then found parameter 1|else no parameter 1| &larr; ''extra'' "|" ''ends else-clause''<br>}}

:::* <nowiki>{{if|{{{1|}}}</nowiki><br>&nbsp; &nbsp; |then found parameter 1 &larr; ''extra newline here''<br>&nbsp; &nbsp; |else noparameter 1|<br>}}

To indent the else-clause, split an [[HTML]]-form comment, as "&lt;!--" with next line as "--&gt;|else...". Unless each then-clause and else-clause is carefully tested, to watch for extra newlines, then the results are likely to cause broken lines, with extra line breaks for each newline. For that reason, a global edit with simple search-and-replace of "<code>{#if:</code>" to "<code>{if||</code>" is likely to leave newline problems, wherever the original markup was wrapped to indent either the else-clause or "}}" of each if-structure. Indenting the then-clause is not a problem.

'''Using P-if syntax:''' A similar if-structure can be coded without '''Template:If''', by using the {P1} and {P2} templates in a "P-if" structure. [[Template:P1]] always returns parameter 1, and P2 returns the 2nd. So, a comparison of 4 versus 3 can be coded using P-if syntax form:

:: Example of <code>#ifexpr</code>: <nowiki>"{{P{{#ifexpr: 4 > 3|1|2}}| then 4 greater| else 4 lower}}"</nowiki>

:: Example of <code>#if</code>: <nowiki>"{{P{{#if:{{{2|x}}}|1|2}}| then {2} set| else {2} empty}}"</nowiki>

 

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