Template:If/doc: Difference between revisions

Revision as of 15:46, 7 September 2012

With this template the parser functions of the ParserFunctions collection with names starting with "#if" can be used in a way such that they do not 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", "exists" or "error" (for #iferror), or empty "||" for a simple if-there (for #if). The template can be repeatedly nested, one inside the other, because the outer-most is completed before running either the then/else inner levels.

This template can be substituted.

Usage

{{if||x| p | q }} gives " p ". Notice the pair of vertical bars surrounding the empty first parameter.

{{if|expr|2<3| p | q }} gives " p "
{{if|eq| u |u| p | q }} gives " p "
{{if|exist| Help:Link | p | q }} gives " q "
{{if|error|{{#expr:x}}| p | q }} gives " p "

Compare:

{{#if:x| p | q }} gives "p"
{{#ifexpr:2<3| p | q }} gives "p"
{{#ifeq: u |u| p | q }} gives "p"
{{#ifexist: Help:Link | p | q }} gives "q"
{{#iferror:{{#expr:x}}| p | q }} gives "p"

The text of either the then-clause or else-clause is only processed and expanded when triggered. Hence, any templates in use are only expanded once the then-clause or else-clause is matched, otherwise they are skipped as merely paired braces, "{{" with "}}".

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:

{{if|{{{1|}}}
|then found parameter 1|else no parameter 1| ← extra "|" ends else-clause
}}

When the else-clause is indented to the next line, a newline (CR/LF) is added:

{{if|{{{1|}}}
|then found parameter 1 ← extra newline here
|else noparameter 1|
}}

To indent the else-clause, split an HTML-form comment, as "|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 "{#if:" to "{if" 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.

@@ Line 1: / Line 1: @@
 {{Documentation subpage}}<includeonly>{{pp-template|small=yes}}</includeonly>
-With this template the [[Help:parser function|parser functions]] of the [[mw:Help:Extension:ParserFunctions|ParserFunctions]] collection with names starting with "#if" can be used in a way such that they do not [[m:Help:Newlines_and_spaces#Stripping_on_expansion|strip spaces and newlines]] from the "then" and "else" part. Spaces still do not affect the outcome of the condition.
+With this template the [[Help:parser function|parser functions]] of the [[mw:Help:Extension:ParserFunctions|ParserFunctions]] collection with names starting with "#if" can be used in a way such that they do not [[m:Help:Newlines_and_spaces#Stripping_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", "exists" or "error" (for #iferror), or empty "||" for a simple if-there (for #if). The template can be repeatedly nested, one inside the other, because the outer-most is completed before running either the then/else inner levels.
 This template can be substituted.
@@ Line 7: / Line 7: @@
 ==Usage==
 *<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 }}"
@@ Line 18: / Line 19: @@
 *<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 }}"
+The text of either the then-clause or else-clause is only processed and expanded when triggered. Hence, any templates in use are only expanded once the then-clause or else-clause is matched, otherwise they are skipped as merely paired braces, "&#123;&#123;" with "}}".
+'''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>}}
+When the else-clause is indented to the next line, a newline (CR/LF) is added:
+:::* <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 "-->|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 "{#if:" to "{if" 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.
 ==See also==