Help:Templates

Complex MediaWiki templates can be a difficult thing to grasp. Editors with a programming background will find few bits of common ground with their language of choice: there are no data types, no loops, no conditionals in the traditional sense of the word. But sometimes these things can be simulated.

[edit] Conditionals

Sometimes, you want to substitute default data if a template parameter is not specified. For example, imagine {{useremail}} with the following contents:

[[User:{{{1}}}|{{{1}}}]] {{ifthen|=<[mailto:{{{2}}}]>|{{{2}}}=(no mail)}}

{{ifthen}} is a very simple generic template:

{{{}}}

It may not be immediately obvious, but {{{}}} is a named parameter. You may have seen template calls like {{supertemp|name=My Template}}. Inside the template, "name" parameter is referenced by {{{name}}}. Our parameter is the same, with one important difference: our parameter name in this case is an empty string.

[edit] In Practice

A standard call to {{Template:useremail}} would look like this:

Function call:	{{useremail|AdamBackstrom|adam@sixohthree.com}}
Template substitution:	[[User:AdamBackstrom|AdamBackstrom]] {{ifthen|=<[mailto:adam@sixohthree.com]>|adam@sixohthree.com=(no mail)}}
Final output:	AdamBackstrom <[1]>

However, the template also allows for cases where the second parameter is included, but empty:

Function call:	{{useremail|AdamBackstrom|}}
Template substitution:	[[User:AdamBackstrom|AdamBackstrom]] {{ifthen|=<[mailto:]>|=(no mail)}}
Final output:	AdamBackstrom (no mail)

Where the first template call defined two variables, {{{}}} and {{{adam@sixohthree.com}}}, the second defined {{{}}} twice in a row. The last declaration takes precedence, so the displayed value is "(no mail)".