File: README

# README

Path: | README
Last Update: | Sun Mar 01 19:13:24 -0700 2009

# Templater

Templater is a system for generating files. Templater has the ability to both copy files from A to B and also to render templates using ERB. Templater consists of four parts:

- Actions (File copying routines, templates generation and directories creation routines).
- Generators (set of rules).
- Manifolds (generator suites).
- The command line interface.

Hierarchy is pretty simple: manifold has one or many public and private generators. Public ones are supposed to be called by end user. Generators have one or more action that specify what they do, where they take files, how they name resulting files and so forth.

## Idea behind Templater

Templater is designed to be flexible and designed to be reflective. Generators created with templater are definitions of what goes where, they provide no interface for the user. This allows you to use templater generators inside your own code, or with the bundled CLI interface, or with your own interface.

## Example

This is how to create a very simple system for generating things:

        module MyGenerators

          extend Templater::Manifold

          class BlogGenerator < Templater::Generator
            # directory this generator uses as source root when searching
                                    # for files, directories, templates
            def self.source_root
              File.join(File.dirname(__FILE__), 'templates')
            end

                                    # uses blog.rbt template (note conventional trailing t)
                                    # placing resulting file to blog.rb relatively to
                                    # destination root
            template :blog, 'blog.rb'

                                    # does simple copy of me.jpg placing resulting file to me.jpg relatively to
                                    # destination root
            file :me, 'me.jpg'

                                    # creates empty directory public/javascripts relatively to
                                    # destination root
                                    empty_directory :javascripts, File.join("public", "javascripts")
          end

          class WikiGenerator < Templater::Generator

            def self.source_root
              File.join(File.dirname(__FILE__), 'templates')
            end

            template :wiki, 'wiki.rb'
            file :img, 'wiki.jpg'

          end

                            # The generators are added to the manifold, and assigned the names 'wiki' and 'blog'.
                            # So you can call them <script name> blog merb-blog-in-10-minutes and
                            # <script name> blog merb-wiki-in-10-minutes, respectively
          add :blog, BlogGenerator
          add :wiki, WikiGenerator

        end

                    # registers manifold with command line interface
        MyGenerators.run_cli Dir.pwd, 'my_generators', '0.1', ARGV

The generator classes override the source_root method to specify where templates will be located. All subclasses of Templater::Generator that have any actions must do this. The `template` and `file` methods add actions to the generator. In the first case, a template that is rendered with ERB and then put in its destination location, in the other case a file that is copied. `empty_directory` action creates empty directory under destination root.

Neither manifolds or generators actually do anything by themselves, they are just abstract representations. The last line invokes the command-line-interface, which fetches the desired generator, tells it to render its templates and checks with the user if there are any problems. The generators can easily be used without the command-line-interface, so it is easy to construct an alternative interface.

## Invoking other generators

Generators can invoke other generators, a WikiBlog generator that creates both a Wiki and a Blog could look like this:

        module MyGenerators

          extend Templater::Manifold

          class WikiBlogGenerator < Templater::Generator

            invoke :wiki
            invoke :blog

          end

          add :wiki_blog, WikiBlogGenerator

        end

It needs no source_root, since it has no actions. The generators are invoked by their name in the manifold, not by their class name; this gives the system a great deal of flexibility.

## Automatically adding actions

It can get tedious to declare each action, instead you can search in a given directory and automatically add all files to your generator, this is done with the glob! function.

        class MyGenerator < Templater::Generator

          def self.source_root
            File.join(File.dirname(__FILE__), 'templates')
          end

          glob!

        end

This will search the source root and add all files as actions.

## Templates

Templates are processed using generator instance scope as binding, so every instance method available on your generator is available in template body.

There are a lot of ways of adding templates:

        template :one_argument, 'source_and_destination.rb'

        template :two_arguments, 'source.rb', 'destination.rb'

        template :block do
          source('source.rb')
          destination(some_instance_method)
        end

        template :expression, 'source.rb' '%some_instance_method%.rb'

In the last example, the characters enclosed in percentage signs will be replaced with the results of the instance method `some_instance_method`

Inside the templates normal ERB can be used. The templates are rendered in the same context as the generator instance, so generator instance methods can be called from inside the template.

        <% if name %>
        puts "My name is <%= name %>"
        <% else %>
        puts "I have no name"
        <% end %>

If you need to render templates where the result should contain actual erb, simply use a double percentage sign, this will prevent the statement from being executed.

        <%= 2 + 2 %>
        <%%= 2 + 2 %>

will result in

        4
        <%= 2 + 2 %>

## Callbacks

Sometimes it might be desirable to add a callback to your actions, an example might be to chmod a binary file after it is created.

        class MyGenerator < Templater::Generator
          template :something, 'something.rb', :after => :chmod

          def chmod(action)
            File.chmod(action.destination, 0750)
          end
        end

## An advanced example

A generator for creating a model class, such as it used by Merb or Rails, could look like this:

        module Merb::Generators

          class ModelGenerator < ComponentGenerator

            def self.source_root
              File.join(super, 'model')
            end

                                    # description end users see next to generator name
            desc <<-DESC
              This is a model generator
            DESC

                                    # options generator takes, their metadata, like description or arguments type
            option :testing_framework, :desc => 'Specify which testing framework to use (spec, test_unit)'
            option :orm, :desc => 'Specify which Object-Relation Mapper to use (none, activerecord, datamapper, sequel)'

                                    # you may use shortcuts for first 4 option positions
            first_argument :name, :required => true
            second_argument :attributes, :as => :hash, :default => {}

            invoke :migration do |generator|
              generator.new(destination_root, options.merge(:model => true), name, attributes)
            end

            template :model, :orm => :none do
              source('model.rbt')
              destination('app/models/' + file_name + '.rb')
            end

            template :model_activerecord, :orm => :activerecord do
              source('model_activerecord.rbt')
              destination('app/models/' + file_name + '.rb')
            end

            template :model_datamapper, :orm => :datamapper do
              source('model_datamapper.rbt')
              destination('app/models/' + file_name + '.rb')
            end

            template :model_sequel, :orm => :sequel do
              source('model_sequel.rbt')
              destination('app/models/' + file_name + '.rb')
            end

            template :spec, :testing_framework => :rspec do
              source('spec.rbt')
              destination('spec/models/' + file_name + '_spec.rb')
            end

            template :test_unit, :testing_framework => :test_unit do
              source('test_unit.rbt')
              destination('test/models/' + file_name + '_test.rb')
            end

            def class_name
              self.name.camel_case
            end

            def test_class_name
              self.class_name + "Test"
            end

            def file_name
              self.name.snake_case
            end

          end

          add :model, ModelGenerator

        end

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