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Tilt

Tilt is a thin interface over a bunch of different Ruby template engines in an attempt to make their usage as generic possible. This is useful for web frameworks, static site generators, and other systems that support multiple template engines but don't want to code for each of them individually.

The following features are supported for all template engines (assuming the feature is relevant to the engine):

Custom template evaluation scopes / bindings
Ability to pass locals to template evaluation
Support for passing a block to template evaluation for "yield"
Backtraces with correct filenames and line numbers
Template file caching and reloading
Fast, method-based template source compilation

The primary goal is to get all of the things listed above right for all template engines included in the distribution.

Support for these template engines is included with the package:

ENGINE                     FILE EXTENSIONS         REQUIRED LIBRARIES
-------------------------- ----------------------- ----------------------------
ERB                        .erb, .rhtml            none (included ruby stdlib)
Interpolated String        .str                    none (included ruby core)
Erubis                     .erb, .rhtml, .erubis   erubis
Haml                       .haml                   haml
Sass                       .sass                   haml (< 3.1) or sass (>= 3.1)
Scss                       .scss                   haml (< 3.1) or sass (>= 3.1)
Less CSS                   .less                   less
Builder                    .builder                builder
Liquid                     .liquid                 liquid
RDiscount                  .markdown, .mkd, .md    rdiscount
Redcarpet                  .markdown, .mkd, .md    redcarpet
BlueCloth                  .markdown, .mkd, .md    bluecloth
Kramdown                   .markdown, .mkd, .md    kramdown
Maruku                     .markdown, .mkd, .md    maruku
RedCloth                   .textile                redcloth
RDoc                       .rdoc                   rdoc
Radius                     .radius                 radius
Markaby                    .mab                    markaby
Nokogiri                   .nokogiri               nokogiri
CoffeeScript               .coffee                 coffee-script (+ javascript)
Creole (Wiki markup)       .wiki, .creole          creole
WikiCloth (Wiki markup)    .wiki, .mediawiki, .mw  wikicloth
Yajl                       .yajl                   yajl-ruby

These template engines ship with their own Tilt integration:

ENGINE                     FILE EXTENSIONS   REQUIRED LIBRARIES
-------------------------- ----------------- ----------------------------
Slim                       .slim             slim (>= 0.7)
Embedded JavaScript                          sprockets
Embedded CoffeeScript                        sprockets
JST                                          sprockets

See TEMPLATES.md for detailed information on template engine options and supported features.

Basic Usage

Instant gratification:

require 'erb'
require 'tilt'
template = Tilt.new('templates/foo.erb')
=> #<Tilt::ERBTemplate @file="templates/foo.rb" ...>
output = template.render
=> "Hello world!"

It's recommended that calling programs explicitly require template engine libraries (like 'erb' above) at load time. Tilt attempts to lazy require the template engine library the first time a template is created but this is prone to error in threaded environments.

The Tilt module contains generic implementation classes for all supported template engines. Each template class adheres to the same interface for creation and rendering. In the instant gratification example, we let Tilt determine the template implementation class based on the filename, but Tilt::Template implementations can also be used directly:

template = Tilt::HamlTemplate.new('templates/foo.haml')
output = template.render

The render method takes an optional evaluation scope and locals hash arguments. Here, the template is evaluated within the context of the Person object with locals x and y:

template = Tilt::ERBTemplate.new('templates/foo.erb')
joe = Person.find('joe')
output = template.render(joe, :x => 35, :y => 42)

If no scope is provided, the template is evaluated within the context of an object created with Object.new.

A single Template instance's render method may be called multiple times with different scope and locals arguments. Continuing the previous example, we render the same compiled template but this time in jane's scope:

jane = Person.find('jane')
output = template.render(jane, :x => 22, :y => nil)

Blocks can be passed to render for templates that support running arbitrary ruby code (usually with some form of yield). For instance, assuming the following in foo.erb:

Hey <%= yield %>!

The block passed to render is called on yield:

template = Tilt::ERBTemplate.new('foo.erb')
template.render { 'Joe' }
# => "Hey Joe!"

Template Mappings

The Tilt module includes methods for associating template implementation classes with filename patterns and for locating/instantiating template classes based on those associations.

The Tilt::register method associates a filename pattern with a specific template implementation. To use ERB for files ending in a .bar extension:

 >> Tilt.register Tilt::ERBTemplate, 'bar'
 >> Tilt.new('views/foo.bar')
 => #<Tilt::ERBTemplate @file="views/foo.bar" ...>

Retrieving the template class for a file or file extension:

 >> Tilt['foo.bar']
 => Tilt::ERBTemplate
 >> Tilt['haml']
 => Tilt::HamlTemplate

It's also possible to register template file mappings that are more specific than a file extension. To use Erubis for bar.erb but ERB for all other .erb files:

 >> Tilt.register Tilt::ErubisTemplate, 'bar.erb'
 >> Tilt.new('views/foo.erb')
 => Tilt::ERBTemplate
 >> Tilt.new('views/bar.erb')
 => Tilt::ErubisTemplate

The template class is determined by searching for a series of decreasingly specific name patterns. When creating a new template with Tilt.new('views/foo.html.erb'), we check for the following template mappings:

views/foo.html.erb
foo.html.erb
html.erb
erb

Fallback mode

If there are more than one template class registered for a file extension, Tilt will automatically try to load the version that works on your machine:

If any of the template engines has been loaded already: Use that one.
If not, it will try to initialize each of the classes with an empty template.
Tilt will use the first that doesn't raise an exception.
If however all of them failed, Tilt will raise the exception of the first template engine, since that was the most preferred one.

Template classes that were registered last would be tried first. Because the Markdown extensions are registered like this:

Tilt.register Tilt::BlueClothTemplate, 'md'
Tilt.register Tilt::RDiscountTemplate, 'md'

Tilt will first try RDiscount and then BlueCloth. You could say that RDiscount has a higher priority than BlueCloth.

The fallback mode works nicely when you just need to render an ERB or Markdown template, but if you depend on a specific implementation, you should use #prefer:

# Prefer BlueCloth for all its registered extensions (markdown, mkd, md)
Tilt.prefer Tilt::BlueClothTemplate

# Prefer Erubis for .erb only:
Tilt.prefer Tilt::ErubisTemplate, 'erb'

When a file extension has a preferred template class, Tilt will always use that class, even if it raises an exception.

Template Compilation

Tilt compiles generated Ruby source code produced by template engines and reuses it on subsequent template invocations. Benchmarks show this yields a 5x-10x performance increase over evaluating the Ruby source on each invocation.

Template compilation is currently supported for these template engines: StringTemplate, ERB, Erubis, Haml, Nokogiri, Builder and Yajl.

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