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copied!<p><code>root</code> is defined on <code>ActionDispatch::Routing::Mapper::Base</code>, which is included by <code>ActionDispatch::Routing::Mapper</code>.</p> <p>There is a little more going on behind the scenes than at first glance. </p> <p>If we look at the definition of <code>draw</code>, we can see why:</p> <pre><code># action_dispatch/routing/route_set.rb def draw(&block) # ... eval_block(block) # ... end </code></pre> <p>The block is converted to a proc (with <code>&</code>) and passed to <code>eval_block</code> which is defined a bit farther down:</p> <pre><code>def eval_block(block) # ... mapper = Mapper.new(self) # ... mapper.instance_exec(&block) end </code></pre> <p>So, as it turns out, <code>yield</code> isn't used at all. The block we pass to <code>Application.routes.draw</code> is just being evaluated in the context of an instance of <code>ActionDispatch::Routing::Mapper</code>.</p> <p>If we add <code>puts self</code> to our <code>config/routes.rb</code>, we can see this in action:</p> <pre><code>Application.routes.draw do puts self end </code></pre> <p>When we run <code>rake routes</code> we get something similar to the following:</p> <pre><code>#<ActionDispatch::Routing::Mapper:0x007feadf52cbd8> # ... </code></pre> <p>For further reading, see:</p> <p><a href="http://ruby-doc.org/core-1.8.7/Object.html#method-i-instance_exec" rel="nofollow">http://ruby-doc.org/core-1.8.7/Object.html#method-i-instance_exec</a> <a href="https://github.com/rails/rails/blob/master/actionpack/lib/action_dispatch/routing/route_set.rb#LC296" rel="nofollow">https://github.com/rails/rails/blob/master/actionpack/lib/action_dispatch/routing/route_set.rb#LC296</a> <a href="https://github.com/rails/rails/blob/master/actionpack/lib/action_dispatch/routing/mapper.rb#LC336" rel="nofollow">https://github.com/rails/rails/blob/master/actionpack/lib/action_dispatch/routing/mapper.rb#LC336</a> <a href="http://rads.stackoverflow.com/amzn/click/1934356476" rel="nofollow">http://www.amazon.com/Metaprogramming-Ruby-Program-Like-Pros/dp/1934356476</a></p>

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