Template:Ifndef
{{ifndef}}
is a compact variant of {{Qif}} for simple
"if defined then void else do" statements
with blank then part. It's the opposite of {{ifdef}}.
Usage
{{Ifndef|value|result}}
yields result if value is blank.
This simple template cannot be substituted, it's used to simplify the following equivalent but somewhat cryptic (names don't matter) code variants:
{{{2{{{1|}}}|}}}{{{result{{{value|}}}|}}}{{{then{{{test|}}}|}}}
Example
| Code | Result |
1 {{Ifndef| |empty}}
|
1 empty |
2 {{Ifndef|x|gotcha}}
|
2 |
3 {{Ifndef| {{{1| }}} | {{{1| }}} undefined}}
|
3 undefined |
4 {{Ifndef| {{{1 }}} | {{{1 }}} bad idea}}
|
4 |
5 {{Ifndef| {{ns:0}} | main namespace}}
|
5 main namespace |
6 {{Ifndef||compare {{Tl|ifdef}} }}
|
6 compare {{ifdef}}
|
7 {{Ifndef|| 2=see=[[#Caveats]] }}
|
7 see=#Caveats |
8 {{Ifndef|| see=[[#Caveats]] }}
|
8 |
Unlike ifdef the minimalistic ifndef cannot reject a missing second parameter.
Caveats
In templates the characters "=" (=) and "|" (|) cannot be used as is in parameters. The numeric character references = and | are often good enough, but for Wiki and XHTML markup the literal characters are required:
- For | template:! (edit•talk•links•history) offers a workaround.
- For = the template parameter mechanism allows
{{ifndef}}resulting in "ok=yes" instead of{{ifndef}}resulting in "".
Substitution works only for {{ifdef}}, but not for {{ifndef}} or {{qif}}.
Source
Copied from the page on meta where it is released under the GFDL.