[ruby-core:71376] [Ruby trunk - Bug #11659] Strange behavior setting previously-undefined local variables with a statement modifier

[mike@oobak.org]

Issue #11659 has been updated by Mike Pastore.


That's not a typo. :-) I wanted to intentionally compare and contrast between a scenario where the same variable was being checked and set (#2) and a scenario where two different variables are in play (#4). 

I understand about the parser now, and in fact found another question/answer on SO that explains it in a similar manner. So it's not a bug, per se. It is kind of a Ruby "WTF", though, and in this humble Rubyist's opinion violates POLA pretty badly. 

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Bug #11659: Strange behavior setting previously-undefined local variables with a statement modifier
https://bugs.ruby-lang.org/issues/11659#change-54747

* Author: Mike Pastore
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.2.3p173 (2015-08-18 revision 51636) [x86_64-linux]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
----------------------------------------
Consider a previously-undefined local variable `var1`:

~~~
irb(main):001:0> if defined?(var1).nil?; var1 = 'default'; end; var1
=> "default"
~~~

Consider previously-undefined local variables `var1` and `var2`:

~~~
irb(main):001:0> var2 = 'default' if defined?(var1).nil?; var2
=> "default"
~~~

Consider a previously-undefined local variable `var3`:

~~~
irb(main):001:0> var3 = 'default' if true; var3
=> "default"
~~~

Consider a previously-undefined local variable `var4`:

~~~
irb(main):001:0> var4 = 'default' if defined?(var4).nil?; var4
=> nil
~~~

Oops! Why is `var4` nil? Logically, considering the prior examples, it should be 'default'. Or are we missing something? 

http://stackoverflow.com/questions/33537059/unless-defined-is-not-working-in-my-code



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