What is this syntax: &:day

Hello,

I've been using Ruby and Rails for about 4 months now and although not often, I've seen this syntax from time to time. What does it mean? For example, in Rails's latest blog post:

Code:

---

latest_transcripts.group_by(&:day).each do |day, transcripts|
 
 p "#{day} -> #{transcripts.map(&:class) * ', '}"
  end
  "2006-03-01 -> Transcript"
  "2006-02-28 -> Transcript"
  "2006-02-27 -> Transcript, Transcript"
  "2006-02-26 -> Transcript, Transcript"

---

See the &:day and &:class? What are these?

This is "to_proc" defined for the Symbol class.

Code:

---

class Symbol
  def to_proc
                proc { |obj, *args| obj.send(self, *args) }
  end
end

p ["abc", "def"].map(&:reverse)
p [1, 2, 3].inject(&:+)

---

See this thread
http://groups.google.com/group/comp....669444207f718b

Wow. Very cool! Ruby never ceases to amaze me :)