Difference between Procs, Blocks, Lambdas in Ruby

proc_block_lambda.rb

# 
# Main difference: Procs are objects, blocks are not.
#
# The '&' tells ruby to turn the proc into a block.
#

class Array
  def map2
    new_ary = []
    self.each do |elem|
      new_ary << yield(elem)
    end
    new_ary
  end
end

p = Proc.new {|elem| elem * 2}

# If you omit '&' an error will be raised
# because the method expect to receive a block.
p([1,2,3].map2(&p))               # => [2, 4, 6]
p([1,2,3].map2 {|elem| elem * 3}) # => [3, 6, 9]

# Difference between procs and lambdas.
# Both are Proc object. The difference is
# shown when returning the objects
p Proc.new {'foo'} # => #<Proc:0x000001030a3ad0@proc_and_block.rb:24>
p lambda {'bar'}   # => #<Proc:0x000001018cba20@proc_and_block.rb:25 (lambda)>