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Mustache

Inspired by ctemplate and et, Mustache is a framework-agnostic way to render logic-free views.

As ctemplates says, "It emphasizes separating logic from presentation: it is impossible to embed application logic in this template language."

Overview

Think of Mustache as a replacement for your views. Instead of views consisting of ERB or HAML with random helpers and arbitrary logic, your views are broken into two parts: a Ruby class and an HTML template.

We call the Ruby class the "view" and the HTML template the "template."

All your logic, decisions, and code is contained in your view. All your markup is contained in your template. The template does nothing but reference methods in your view.

This strict separation makes it easier to write clean templates, easier to test your views, and more fun to work on your app's front end.

Why?

I like writing Ruby. I like writing HTML. I like writing JavaScript.

I don't like writing ERB, Haml, Liquid, Django Templates, putting Ruby in my HTML, or putting JavaScript in my HTML.

Usage

Quick example:

>> require 'mustache'
=> true
>> Mustache.render("Hello {{planet}}", :planet => "World!")
=> "Hello World!"

We've got an examples folder but here's the canonical one:

class Simple < Mustache
  def name
    "Chris"
  end

  def value
    10_000
  end

  def taxed_value
    value - (value * 0.4)
  end

  def in_ca
    true
  end
end

We simply create a normal Ruby class and define methods. Some methods reference others, some return values, some return only booleans.

Now let's write the template:

Hello {{name}}
You have just won ${{value}}!
{{#in_ca}}
Well, ${{taxed_value}}, after taxes.
{{/in_ca}}

This template references our view methods. To bring it all together, here's the code to render actual HTML;

Simple.render

Which returns the following:

Hello Chris
You have just won $10000!
Well, $6000.0, after taxes.

Simple.

Tag Types

Tags are indicated by the double mustaches. {{name}} is a tag. Let's talk about the different types of tags.

Variables

The most basic tag is the variable. A {{name}} tag in a basic template will try to call the name method on your view. If there is no name method, an exception will be raised.

All variables are HTML escaped by default. If you want, for some reason, to return unescaped HTML you can use the triple mustache: {{{name}}}.

Boolean Sections

A section begins with a pound and ends with a slash. That is, {{#person}} begins a "person" section while {{/person}} ends it.

If the person method exists and calling it returns false, the HTML between the pound and slash will not be displayed.

If the person method exists and calling it returns true, the HTML between the pound and slash will be rendered and displayed.

Enumerable Sections

Enumerable sections are syntactically identical to boolean sections in that they begin with a pound and end with a slash. The difference, however, is in the view: if the method called returns an enumerable, the section is repeated as the enumerable is iterated over.

Each item in the enumerable is expected to be a hash which will then become the context of the corresponding iteration. In this way we can construct loops.

For example, imagine this template:

{{#repo}}
  <b>{{name}}</b>
{{/repo}}

And this view code:

def repo
  Repository.all.map { |r| { :name => r.to_s } }
end

When rendered, our view will contain a list of all repository names in the database.

As a convenience, if a section returns a hash (as opposed to an array or a boolean) it will be treated as a single item array.

With the above template, we could use this Ruby code for a single iteration:

def repo
  { :name => Repository.first.to_s }
end

This would be treated by Mustache as functionally equivalent to the following:

def repo
  [ { :name => Repository.first.to_s } ]
end

Comments

Comments begin with a bang and are ignored. The following template:

<h1>Today{{! ignore me }}.</h1>

Will render as follows:

<h1>Today.</h1>

Partials

Partials begin with a less than sign, like {{< box}}.

If a partial's view is loaded, we use that to render the HTML. If nothing is loaded we render the template directly using our current context.

In this way partials can reference variables or sections the calling view defines.

Set Delimiter

Set Delimiter tags start with an equal sign and change the tag delimiters from {{ and }} to custom strings.

Consider the following contrived example:

* {{ default_tags }}
{{=<% %>=}}
* <% erb_style_tags %>
<%={{ }}=%>
* {{ default_tags_again }}

Here we have a list with three items. The first item uses the default tag style, the second uses erb style as defined by the Set Delimiter tag, and the third returns to the default style after yet another Set Delimiter declaration.

According to ctemplates, this "is useful for languages like TeX, where double-braces may occur in the text and are awkward to use for markup."

Custom delimiters may not contain whitespace or the equals sign.

Dict-Style Views

ctemplate and friends want you to hand a dictionary to the template processor. Mustache supports a similar concept. Feel free to mix the class-based and this more procedural style at your leisure.

Given this template (winner.html):

Hello {{name}}
You have just won ${{value}}!

We can fill in the values at will:

view = Winner.new
view[:name] = 'George'
view[:value] = 100
view.render

Which returns:

Hello George
You have just won $100!

We can re-use the same object, too:

view[:name] = 'Tony'
view.render
Hello Tony
You have just won $100!

Templates

A word on templates. By default, a view will try to find its template on disk by searching for an HTML file in the current directory that follows the classic Ruby naming convention.

TemplatePartial => ./template_partial.html

You can set the search path using Mustache.template_path. It can be set on a class by class basis:

class Simple < Mustache
  self.template_path = File.dirname(__FILE__)
  ... etc ...
end

Now Simple will look for simple.html in the directory it resides in, no matter the cwd.

If you want to just change what template is used you can set Mustache.template_file directly:

Simple.template_file = './blah.html'

Mustache also allows you to define the extension it'll use.

Simple.template_extension = 'xml'

Given all other defaults, the above line will cause Mustache to look for './blah.xml'

Feel free to set the template directly:

Simple.template = 'Hi {{person}}!'

Or set a different template for a single instance:

Simple.new.template = 'Hi {{person}}!'

Whatever works.

Helpers

What about global helpers? Maybe you have a nifty gravatar function you want to use in all your views? No problem.

This is just Ruby, after all.

module ViewHelpers
  def gravatar(email, size = 30)
    gravatar_id = Digest::MD5.hexdigest(email.to_s.strip.downcase)
    gravatar_for_id(gravatar_id, size)
  end

  def gravatar_for_id(gid, size = 30)
    "#{gravatar_host}/avatar/#{gid}?s=#{size}"
  end

  def gravatar_host
    @ssl ? 'https://secure.gravatar.com' : 'http://www.gravatar.com'
  end
end

Then just include it:

class Simple < Mustache
  include ViewHelpers

  def name
    "Chris"
  end

  def value
    10_000
  end

  def taxed_value
    value - (value * 0.4)
  end

  def in_ca
    true
  end
end

Great, but what about that @ssl ivar in gravatar_host? There are many ways we can go about setting it.

Here's on example which illustrates a key feature of Mustache: you are free to use the initialize method just as you would in any normal class.

class Simple < Mustache
  include ViewHelpers

  def initialize(ssl = false)
    @ssl = ssl
  end

  ... etc ...
end

Now:

Simple.new(request.ssl?).render

Convoluted but you get the idea.

Sinatra

Mustache ships with Sinatra integration. Please see lib/mustache/sinatra.rb or http://defunkt.github.com/mustache/classes/Mustache/Sinatra.html for complete documentation.

An example Sinatra application is also provided: http://github.com/defunkt/mustache-sinatra-example

Vim

Thanks to Juvenn Woo for mustache.vim. It is included under the contrib/ directory.

Installation

Gemcutter

$ gem install mustache

Rip

$ rip install git://github.com/defunkt/mustache.git

Acknowledgements

Thanks to Tom Preston-Werner for showing me ctemplate and Leah Culver for the name "Mustache."

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