#! ruby19

ADDR = %r{[-.\w]+@[-.\w]+}
email = DATA.read.freeze

# 1. Java style

subst = {}

puts email.gsub(ADDR) {|match|
  if subst.has_key? match
    subst[match]
  else
    subst[match] = "<<MAIL #{subst.size}>>"
  end
}

# 2. a little more sophisticated

subst = {}

puts email.gsub(ADDR) {|match|
  subst.fetch(match) {|k| subst[k] = "<<MAIL #{subst.size}>>" }
}

# 3. o||=erator

subst = {}

puts email.gsub(ADDR) {|match|
  subst[match] ||= "<<MAIL #{subst.size}>>"
}

# 4. outsourcing

subst = Hash.new {|h,k| h[k] = "<<MAIL #{h.size}>>"}

puts email.gsub(ADDR) {|match| subst[match]}

# 5. getting tricky

subst = Hash.new {|h,k| h[k] = "<<MAIL #{h.size}>>"}

puts email.gsub(ADDR, &subst.method(:[]))

# 6. even shorter with a general solution

class Object
  def to_proc(m = :[])
    method(m).to_proc
  end
end

subst = Hash.new {|h,k| h[k] = "<<MAIL #{h.size}>>"}

puts email.gsub(ADDR, &subst)

# 7. golf

puts email.gsub(ADDR, &Hash.new {|h,k| h[k] = "<<MAIL #{h.size}>>"})

# 8. the fun begins

Name = Struct.new :forename, :surname

# unfortunately this does not work with the default Struct.[]
def Name.[](a)
  new(*a)
end

p [
  ["John", "Doe"],
  ["John", "Cleese"],
  ["Mickey", "Mouse"],
].map(&Name)

def Name.create(a)
  new(*a)
end

p [
  ["John", "Doe"],
  ["John", "Cleese"],
  ["Mickey", "Mouse"],
].map(&Name.to_proc(:create))

__END__
From some-user@his.domain.com
To: whatever@somewhere.else
Cc: foo@bar.com, some-user@his.domain.com
Subject: I thought you should know

Hi,

  id you know that foo@bar.com recently sent me an email
at my address some-user@his.domain.com?

Cheers

--
  mailto:some-user@his.domain.com
EOM