Revision as of 16:43, 2 November 2020 view source Caleb Cooper (talk \| contribs) Bureaucrats, Interface administrators, Administrators 9,367 edits Created page with "{{stack\|{{Documentation subpage}}{{high-risk}}}}{{Commons Import}} With this template the parser functions of the mw:Help:Extension:ParserFunctions\|..."		Latest revision as of 16:51, 2 November 2020 view source Caleb Cooper (talk \| contribs) Bureaucrats, Interface administrators, Administrators 9,367 edits No edit summary
Line 1: {{stack\|{{Documentation subpage}}{{high-risk}}}}{{Commons Import}} With this template the [[Wikipedia:Help:parser function\|parser functions]] of the [[mwmediawikiwiki: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", "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. This template can be substituted, when the expression or comparison will not change. Functionally, a lead-space character is stored, internally, as a simple blank character. Note, in many cases a null nowiki tag ("<nowiki/>") could be used, without [[Template:If]], to allow a lead-space (such as "<nowiki/> xx") anywhere, but the internal storage puts a 43-character marker for "<nowiki/>" in string length. However, there is no extra expansion depth for a nowiki-tag, such as in trailing space, "zz <nowiki/>". Line 35: \|else noparameter 1\| }}</syntaxhighlight> To indent the else-clause, split an [[Wikipedia:HTML\|HTML]]-form comment, as "<code><!--</code>" with next line as "<code>-->\|else...</code>". 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. ==Performance considerations== Because [[Template:If]] must prepare the parameters for <code>#if, #ifeq, #ifexpr,</code> (etc.) there is a slight overhead when using it. It has been timed to run at speeds of 290 instances per second, so 29 uses would take only 0.1 s, a tenth of a second to run, to make 29 comparisons. Each nested use adds 5 levels to the template expansion depth, so 7 nested if-templates would use 35 levels (57) of the [[mmediawikiwiki:Help:Expansion_depth\|41-level limit]]. '''Using P-if syntax:''' A similar if-structure can be coded without '''Template:If''', by using the {{tlx\|P1}} and {{tlx\|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: Line 49: ==See also== [[m:Template:If]] [[Template:Ifnotempty]] - for simplicity and to reduce the limitations due to the expansion depth limit, this is a separate template corresponding to #if only. [[Template:Switch]], for a default result *[[Wikipedia:Help:Conditional expressions\|Help:Conditional expressions]] <includeonly>{{Sandbox other\|\| [[Category:If-then-else templates]]

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