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Permanent binding error in Ruby?

We caught some code in Ruby that seems weird, and I was wondering if anyone could explain this:

$ irb
irb(main):001:0> APPLE = 'aaa'
=> "aaa"
irb(main):002:0> banana = APPLE
=> "aaa"
irb(main):003:0> banana << 'bbb'
=> "aaabbb"
irb(main):004:0> banana
=> "aaabbb"
irb(main):005:0> APPLE
=> "aaabbb"

Catch it? A constant was added at the same time that there was a local variable.

Known behavior? Expected?

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4 answers

Catch it? A constant was added at the same time that there was a local variable.

No, it was not added, and there was no local variable.

One object referenced by both a constant and a local variable is added, but neither the constant nor the local variable has been changed. You cannot change or change a variable or constant in Ruby (at least not as your question implies), the only thing you can change is objects.

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ORIG = ['Hello']
CLONE = ORIG.dup.freeze
CLONE[0] << ', World!'
CLONE # => ['Hello, World!']

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>> APPLE = 'aaa'
=> "aaa"
>> banana = APPLE
=> "aaa"
>> APPLE.freeze
=> "aaa"
>> banana.frozen?
=> true
>> banana << 'bbb'
TypeError: can't modify frozen string
    from (irb):5:in `<<'
    from (irb):5
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If you look at it this way, the behavior is obvious and necessary; Apple is a pointer to a string object, as well as a banana. Then you edit the object that the banana points to. Apple points to the same object, so the change is reflected there.

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