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    <p>This is the Ruby block (Ruby's name for an anonymous function) syntax. And <code>key</code>, <code>value</code> are nothing but the arguments passed to the anonymous function. </p> <p><code>Hash#each</code> takes one parameter: A function which has 2 parameters, <code>key</code> and <code>value</code>.</p> <p>So if we break it down into parts, this part of your code: <code>h.each</code>, is calling the <code>each</code> function on <code>h</code>. And this part of your code:</p> <pre><code>do |key, value| # Iterate through the key/value pairs print "#{value}:#{key}; " # Note variables substituted into string end # Prints "1:one; 2:two; 3:three; </code></pre> <p>is the function passed to <code>each</code> as an argument and <code>key</code>, <code>value</code> are arguments passed to this function. It doesn't matter what you name them, first argument expected is <em>key</em> and second argument expected is <em>value</em>.</p> <p>Lets draw some analogies. Consider a basic function:</p> <pre><code> def name_of_function(arg1, arg1) # Do stuff end # You'd call it such: foo.name_of_function bar, baz # bar is becomes as arg1, baz becomes arg2 # As a block: ooga = lambda { |arg1, arg2| # Do stuff } # Note that this is exactly same as: ooga = lambda do |arg1, arg2| # Do stuff end # You would call it such: ooga.call(bar, baz) # bar is becomes as arg1, baz becomes arg2 </code></pre> <p>So your code can also be written as:</p> <pre><code>print_key_value = lambda{|arg1, arg2| print "#{arg1}:#{arg2}"} h = { :one =&gt; 1, :two =&gt; 2 } h.each &amp;print_key_value </code></pre> <p>There are multiple ways in which the code inside a block can be executed:</p> <pre><code> yield yield key, value # This is one possible way in which Hash#each can use a block yield item block.call block.call(key, value) # This is another way in which Hash#each can use a block block.call(item) </code></pre>
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