Here are the unit tests I added:

  def test_pass_args
    original = ["hello world", "hallo wereld", "ciao mondo"]
    expected = %w[hell hall ciao]
    assert_equal(expected, original.map_by_slice(0,4))
  end

  def test_pass_block
    original = ["hello world", "hallo wereld", "ciao mondo"]
    expected = ["[hello ]world”, “[hallo ]wereld”, “[ciao ]mondo”]
    assert_equal(expected, original.map_by_gsub(/^(.*)\s/) {|first_word| “[#{first_word}]” })
  end

Is there a particular reason why you don’t pass the arguments and block magic to the mapped method? For more fun I modified line 33 to:

self.send(iterator) { |item| item.send(method, *args, &block) }

and ran these tests:

require ‘map_by_method’
a = ["hello world", "hallo wereld", "ciao mondo"]
puts a.map_by_capitalize
puts a.map_by_center(30)
a.map_by_scan(/^(.*)\s(.*)$/) {|x,y| print y, “.”, x, ” — ” }

which outputs:

Hello world
Hallo wereld
Ciao mondo
hello world
hallo wereld
ciao mondo
world.hello — wereld.hallo — mondo.ciao –

performance wise this gem works pretty well. Much nicer magic this compared to Symbol#to_proc.

Best regards,
Lawrence Pit