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[Docs] Use of $. to access global context from anywhere

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See #804, http://discuss.gohugo.io/t/templates-multiple-parameters/600/3
and http://stackoverflow.com/questions/16734503/access-out-of-loop-value-inside-golang-templates-loop
for related discussions.
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Anthony Fok 2015-01-21 00:35:12 -07:00
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51
docs/content/templates/go-templates.md
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@ -249,24 +249,47 @@ Alternatively, use the backtick (`` ` ``) to quote the IE conditional comments,
## Context (a.k.a. the dot) ## Context (a.k.a. the dot)
The most easily overlooked concept to understand about Go templates is that `{{ . }}` The most easily overlooked concept to understand about Go templates is that `{{ . }}`
always refers to the current context. In the top level of your template this always refers to the current context. In the top level of your template, this
will be the data set made available to it. Inside of a iteration it will have will be the data set made available to it. Inside of a iteration, however, it will have
the value of the current item. When inside of a loop the context has changed. the value of the current item. When inside of a loop, the context has changed:
`.` will no longer refer to the data available to the entire page. If you need `{{ . }}` will no longer refer to the data available to the entire page. If you need
to to
access this from within the loop, you will likely want to set it to a variable access this from within the loop, you will likely want to do one of the following:
instead of depending on the context.
**Example:** 1. Set it to a variable instead of depending on the context. For example:
{{ $title := .Site.Title }} {{ $title := .Site.Title }}
{{ range .Params.tags }} {{ range .Params.tags }}
<li> <a href="{{ $baseurl }}/tags/{{ . | urlize }}">{{ . }}</a> - {{ $title }} </li> <li>
{{ end }} <a href="{{ $baseurl }}/tags/{{ . | urlize }}">{{ . }}</a>
- {{ $title }}
</li>
{{ end }}
Notice how once we have entered the loop the value of `{{ . }}` has changed. We Notice how once we have entered the loop the value of `{{ . }}` has changed. We
have defined a variable outside of the loop so we have access to it from within have defined a variable outside of the loop so we have access to it from within
the loop. the loop.
2. Use `$.` to access the global context from anywhere.
Here is an equivalent example:
{{ range .Params.tags }}
<li>
<a href="{{ $baseurl }}/tags/{{ . | urlize }}">{{ . }}</a>
- {{ $.Site.Title }}
</li>
{{ end }}
This is because `$`, a special variable, is set to the starting value
of `.` the dot by default,
a [documented feature](http://golang.org/pkg/text/template/#hdr-Variables)
of Go text/template. Very handy, eh?
> However, this little magic would cease to work if someone were to
> mischievously redefine `$`, e.g. `{{ $ := .Site }}`.
> *(No, don't do it!)*
> You may, of course, recover from this mischief by using `{{ $ := . }}`
> in a global context to reset `$` to its default value.
# Hugo Parameters # Hugo Parameters