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Last modified 8 months ago Last modified on 10/04/11 11:27:09

Inversion

Inversion is a templating system for Ruby. It uses the "Inversion of Control" principle to decouple the contents and structure of templates from the code that uses them, making it easier to separate concerns, keep your tests simple, and avoid polluting scopes with ephemeral data.

Details

Inversion, like most other templating systems, works by giving you a way of defining the static parts of your output, and then letting you combine that at a later point with the dynamic parts:

Create the template and use it to render an exciting message: 

tmpl = Inversion::Template.new( "Hello, <?attr name ?>!" )
tmpl.name = "World"
puts tmpl.render

The <?attr name ?> tag defines the name accessor on the template object, the value of which is substituted for any occurrences of name in the template: 

Hello, World!

This by itself isn't fantastically useful, but it does illustrate one of the ways in which Inversion is different: the program and the template share data through an API, instead of through a complex data structure, which establishes a clear delineation between what responsibility is the program's and which is the template's. The program doesn't have to know how the view uses the data it's given, and tests of the controller can substitute a Mock Object for the template to test the interaction between the two instead of having to match patterns in the eventual output like an integration test.

You can also interact with the values set in the template: 

Name: <?attr employee.full_name ?>

This will call the #full_name method on whatever is set as the employee attribute when rendered, and the result will take the place of the tag.

Inversion also comes with a collection of other tags that provide flow control, exception-handling, etc.

Here's a slightly more complex example: Say we have a layout template that contains all the boilerplate, navigation, etc. for the site, and then an <?attr body ?> somewhere in the content area for the content specific to each view: 

layout = Inversion::Template.load( 'templates/layout.tmpl' )

Then there's a view template that displays a bulleted list of article titles: 

<!-- articlelist.tmpl -->
<section id="articles">
  <ul>
  <?for article in articles ?>
    <li><?call article.title ?></li>
  <?end for ?>
  </ul>
</section>

Loading this template results in a Ruby object whose API contains one method: #articles. To render the view, we just call that accessor with instances of an Article domain class we've defined elsewhere, and then drop the 'articlelist' template into the layout and render them: 

alist = Inversion::Template.load( 'templates/articlelist.tmpl' )
alist.articles = Articles.latest( 10 )

layout.body = alist
puts layout.render

The for tag in the articlelist will iterate over the enumerable Articles and generate an <li> for each one. The resulting template object will be set as the body of the layout template, and stringified when the enclosing template is rendered. Templates can be nested this way as deeply as you like.

For detailed tag documentation and examples, see the ​online manual, or browse the ​API docs.

References

Downloads

Development

You can check out the current development source with Mercurial like so: 

hg clone http://repo.deveiate.org/Inversion

We're also keeping some notes as we work which may give you a better idea of what we're doing, and as we decide on upcoming features, we'll add them to the milestones in the roadmap.

Trac Information

For a complete list of local wiki pages, see TitleIndex.