Issue #11659 has been updated by Hans Mackowiak.



~~~
var2 = 'default' if defined?(var1).nil?; var2
~~~

because you got a typo for var2, see the var1 inside.



~~~
var4 = 'default' if defined?(var4).nil?; var4
~~~

the problem there is that var got defined from the parser before the code is run, so when it does check for defined, var4 is already defined




also checkout:

~~~
var = "ok" if false; var #=> nil
~~~


----------------------------------------
Bug #11659: Strange behavior setting previously-undefined local variables with a statement modifier
https://bugs.ruby-lang.org/issues/11659#change-54717

* 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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