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Generic interface to multiple Ruby template engines

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README.md

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              none (included ruby stdlib)
Interpolated String        .str              none (included ruby core)
Haml                       .haml             haml
Sass                       .sass             haml
Less CSS                   .less             less
Builder                    .builder          builder
Liquid                     .liquid           liquid
RDiscount                  .markdown         rdiscount
RedCloth                   .textile          redcloth
RDoc                       .rdoc             rdoc
Radius                     .radius           radius

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 'bar', Tilt::ERBTemplate
 >> 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 'bar.erb', Tilt::ErubisTemplate
 >> 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:

  1. views/foo.html.erb
  2. foo.html.erb
  3. html.erb
  4. erb

Tilt::register can also be used to select between alternative template engines. To use Erubis instead of ERB for .erb files:

Tilt.register 'erb', Tilt::ErubisTemplate

Or, use BlueCloth for markdown instead of RDiscount:

Tilt.register 'markdown', Tilt::BlueClothTemplate

Template Compilation

Tilt can compile generated Ruby source code produced by template engines and reuse 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, and Builder.

To enable template compilation, the Tilt::CompileSite module must be mixed in to the scope object passed to the template's #render method. This can be accomplished by including (with Module#include) the module in the class used for scope objects or by extending (with Object#extend) scope objects before passing to Template#render:

require 'tilt'

template = Tilt::ERBTemplate.new('foo.erb')

# Slow. Uses Object#instance_eval to process template
class Scope
end
scope = Scope.new
template.render(scope)

# Fast. Uses compiled template and Object#send to process template
class Scope
  include Tilt::CompileSite
end
scope = Scope.new
template.render(scope)

# Also fast, though a bit a slower due to having to extend each time
scope = Object.new
scope.extend Tilt::CompileSite
template.render(scope)

When the Tilt::CompileSite module is not present, template execution falls back to evaluating the template from source on each invocation.

LICENSE

Tilt is Copyright (c) 2010 Ryan Tomayko and distributed under the MIT license. See the COPYING file for more info.

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