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    <p>Like Philip explained in his answer when using rake the colon defines the seperator between namespaces/tasks</p> <p>When using <code>rails g(enerate)</code> it's basically the same. The difference is that Rails generators aren't defined with rake's DSL, instead they're classes.</p> <p>But to answer your initial Questions: The Colon works as seperator, in both cases, that's it.</p> <p>In the code the only thing what it's important for is splitting up the string: <a href="https://github.com/rails/rails/blob/4-0-stable/railties/lib/rails/generators.rb#L124" rel="nofollow">https://github.com/rails/rails/blob/4-0-stable/railties/lib/rails/generators.rb#L124</a></p> <p>You can find some more infos about generators and how to create your one ones (which definetley will help you understanding the mechanics behind it) in the official <a href="http://guides.rubyonrails.org/generators.html" rel="nofollow">Ruby on Rails Guides</a> </p> <p>//EDIT Ok, let's take a closer look at the generator lookup process:</p> <p>First of all there is <a href="https://github.com/rails/rails/blob/master/railties/lib/rails/generators.rb#L152" rel="nofollow"><code>Rails::Generators.invoke</code></a></p> <p>It receives the namespaces passed on the CLI and split's it up (using the colon)</p> <pre><code> names = namespace.to_s.split(':') </code></pre> <p>then it get's the according class by passing the last part of the passed namespace (the actual generator name) and the remaining part joined with a colon again (the namespace path, in our case it's <em>devise</em>) to <a href="https://github.com/rails/rails/blob/4-0-stable/railties/lib/rails/generators.rb#L124" rel="nofollow"><code>Rails::Generators::Base.find_by_namespace</code></a></p> <pre><code> if klass = find_by_namespace(names.pop, names.any? &amp;&amp; names.join(':')) </code></pre> <p>This method again will join the base (namespace path) and name (generator name) and push it to an array:</p> <pre><code>lookups = [] lookups &lt;&lt; "#{base}:#{name}" if base </code></pre> <p>after that it calls <a href="https://github.com/rails/rails/blob/4-0-stable/railties/lib/rails/generators.rb#L272" rel="nofollow"><code>Rails::Generators.lookup</code></a> which will lookup the classes to invoke for the called generator:</p> <pre><code>lookup(lookups) </code></pre> <p>which will again will call <a href="https://github.com/rails/rails/blob/4-0-stable/railties/lib/rails/generators.rb#L308" rel="nofollow"><code>Rails::Generators.namepaces_to_paths</code></a></p> <p>There's no big magic in that method, it'll simply return an array of two possible source paths for the invoked generator in our case these two are "devise/install/install" and "devise/install".</p> <p>Whereby those aren't the actual paths rails will check, they are only the part's of it that are depend on the namespace:generator construct.</p> <p>The <code>lookup</code> method will now take those two, let's call them subpaths, and check for files to require at the following places:</p> <ol> <li>rails/generators/devise/install/install_generator</li> <li>generators/devise/install/install_generator</li> <li>rails/generators/devise/install_generator</li> <li>generators/devise/install_generator</li> </ol> <p>in our case the second path is the desired file, rails require's it and through that the <a href="https://github.com/rails/rails/blob/4-0-stable/railties/lib/rails/generators/base.rb#L225" rel="nofollow"><code>inherited</code></a> (<a href="http://www.ruby-doc.org/core-2.0/Class.html#method-i-inherited" rel="nofollow">more about that callback</a> callback on <a href="https://github.com/rails/rails/blob/4-0-stable/railties/lib/rails/generators/base.rb" rel="nofollow"><code>Rails::Generators::Base</code></a> will get called since <a href="https://github.com/plataformatec/devise/blob/master/lib/generators/devise/install_generator.rb" rel="nofollow"><code>Devise::Generators::InstallGenerator</code></a> inherits from it.</p> <p>This will add the Class to the <code>subclasses</code> array of <code>Rails::Generators</code> which is mapped to an Hash which will have the format { namespace => klass } and so rails is finally able to get the desired Generator Class</p> <p><a href="https://github.com/rails/rails/blob/4-0-stable/railties/lib/rails/generators.rb#L142" rel="nofollow"><code>klass = namespaces[namespace]</code></a></p> <p>and start it</p> <p><a href="https://github.com/rails/rails/blob/4-0-stable/railties/lib/rails/generators.rb#L156" rel="nofollow"><code>klass.start(args, config)</code></a></p>
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    1. USManuel Görlich
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    1. COThat helps a lot. However I am still confused on how it works in the generate case. I've actually read this ruby on rails guide that you mentioned many times, but I still don't get how it works for the devise code that I showed Phillip. Any help will be extremely appreciated.
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      1. USDanilo Faria
    2. COThanks very much, that definitely solves my problem!
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