What does map(&:name) mean in Ruby?

Question

I found this code in a RailsCast:

def tag_names
  @tag_names || tags.map(&:name).join(\' \')
end

What does the (&:name)

Answer 1

While let us also note that ampersand #to_proc magic can work with any class, not just Symbol. Many Rubyists choose to define #to_proc on Array class:

class Array
  def to_proc
    proc { |receiver| receiver.send *self }
  end
end

# And then...

[ 'Hello', 'Goodbye' ].map &[ :+, ' world!' ]
#=> ["Hello world!", "Goodbye world!"]

Ampersand & works by sending to_proc message on its operand, which, in the above code, is of Array class. And since I defined #to_proc method on Array, the line becomes:

[ 'Hello', 'Goodbye' ].map { |receiver| receiver.send( :+, ' world!' ) }