Array.each_with_index doesn't run as expected

Question

I redefined Array#replace like follows.

require 'test/unit'  
class Array  
  def replace (from, to)  
    each_with_index do |e, i|  
      self[i] = to if e = from  
    end  
  end  
end  

class TestDriver <Test::Unit::TestCase  
  def test_replace  
    book_topic = ['html', 'java', 'css']  
    book_topic.replace('java', 'ruby')  
    result_topic = ['html', 'ruby', 'css']  
    assert_equal book_topic, result_topic  
  end  
end

When I run that test case, it asserts the book_topic is ['html', 'ruby', 'ruby']. I have no idea about the result of book_topic. Can anyone tell me why?

Dogbert · Accepted Answer · 2013-04-28 15:31:34Z

8

You missed an = in e == from.

self[i] = to if e == from

PS: I hope you know the pros/cons of overriding core methods like this.

answered Apr 28, 2013 at 15:31

Dogbert

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3 Comments

madper Over a year ago

ohhhhhh. I'm foolish... Yes, I know I'm overriding a core class. Thank you very very much!

Charles Caldwell Over a year ago

@madper Based on your comment, you should probably mark this as the answer.

madper Over a year ago

@CharlesCaldwell, Sure. Sorry for late. When I mark this as answer, it said I should wait 9minutes. And I forget it after a while. I think I got Alzheimerdisease. :-)

Denis de Bernardy · Accepted Answer · 2013-04-28 15:36:52Z

2

Consider using map or map! instead of overriding Array's replace method.

>> [1,2,3].map { |a| a == 1 ? 2 : a }
=> [2, 2, 3]

answered Apr 28, 2013 at 15:36

Denis de Bernardy

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