Ruby statement modifiers behave differently than conditional statements

Re:Ruby statement modifiers behave differently than conditio... by Locke on Monday December 28, 2009 @12:27PM (#1018902)

Yes, they are different. For example:

    def ex1
      a = 5

      if a
        puts "a: #{a}"
      end
    end

    def ex2
      if a = 5
        puts "a: #{a}"
      end
    end

    def ex3
      puts "a: #{a}"  if a = 5
    end

If we start with the code in ex1 and decide to shorten it, ex2 is okay (although some people don't care for assignment in a conditional because it could be confused for a typo). But, ex3 will raise an exception that 'a' has not been defined.

I've just internalized using the longer form when using assignment in a conditional.

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Re:Ruby statement modifiers behave differently than conditio... by chief on Monday December 28, 2009 @01:50PM (#1019102)

I think the article is wrong. His rewrite on line 06. should use if instead of unless.

  $ irb
  >> b
  NameError: undefined local variable or method `b' for main:Object
  	from (irb):1
  >> if defined? b
  >>   b = 5
  >> end
  => nil
  >> b
  => nil
  >> defined? b
  => "local-variable"

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Re:Ruby statement modifiers behave differently than conditio... by angilly on Monday December 28, 2009 @02:05PM (#1019126)

No, it's using unless like I intended. But your example also demonstrates the weird behavior. As a few people have pointed out here and over in the post comments, the issue at hand isn't so much about statement modifiers as it is about how Ruby 'defines' local variables.

Take this for example:

  ra:~$ irb
  a = irb(main):001:0> a = b
  NameError: undefined local variable or method `b' for main:Object
  	from (irb):1
  irb(main):002:0> defined? a
  => "local-variable"
  irb(main):003:0>

It just so happens that using statement modifiers in the way I tried using them brings this behavior to light.

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