Exploring Ruby's black magic #1

sigil.rb

# This Enumerator#sum example from the Ruby docs is pure black magic to me:
#
#     "a\nb\nc".each_line.lazy.map(&:chomp).sum("")  #=> "abc"
#
# So I’mma figure out how and why it works by implementing a version of it.

# Sigils are Symbol-like objects that can be converted to Procs.
class Sigil
  def initialize(name)
    @name = name
  end

  def to_sym
    @name.to_sym
  end

  def to_proc
    puts "self => #{self.inspect}"
    Proc.new { |obj, args| obj.send(self.to_sym, *args) }
  end
end

sigil = Sigil.new 'upcase'
block = s.to_proc

block.call 'a wild foo appeared!' # => "A WILD FOO APPEARED!"
%w(foo bar baz).map &sigil        # => ["FOO", "BAR", "BAZ"]