Uninitialized variables
Posted by Sergey Enin 31 July 2011 at 04:37
In comment to one of previous posts wrote how usually ruby developers solve uninitliazed variables problem in conditions:
if (!!@a)
This works, cause:
1) in Ruby, everything evaluated as TRUE, but not FALSE or NIL!
2) > !nil
=> true
#so, !!nil => false;
3) in Ruby uninitialized instance variables evaluated as nil;
I dont believe it is best way(though possible). Consider, that if you are cared programmer and develop with "ruby -w" ruby will write you warning.
However, I decided to review uninitialized variables in ruby:
@@a - Class variables:
ruby-1.9.2-p136 :004 > @@a
NameError: uninitialized class variable @@a in Object
@a - Instance variables:
ruby-1.9.2-p136 :003 > @a
=> nil
(if -w - then cause warning)
$a - Global variables:
ruby-1.9.2-p136 :011 > $a
=> nil
(if -w - then cause warning)
a - Local variables:
ruby-1.9.2-p136 :001 > a
NameError: undefined local variable or method `a' for main:Object
but
if we will do
ruby-1.9.2-p136 :003 > a = 2 if false
=> nil
ruby-1.9.2-p136 :004 > a
=> nil
A - Constants:
ruby-1.9.2-p136 :002 > A
NameError: uninitialized constant Object::A
Thank you.
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