# Weird variable scope behaviour **URL:** \ **Category:** Ruby\ **Created:** [September 23, 2007, 12:36am UTC](https://www.ruby-forum.com/t/weird-variable-scope-behaviour/115276 "2007-09-23T00:36:19Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![maz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@maz](https://www.ruby-forum.com/u/maz)\ **Post date:** [September 23, 2007, 12:36am UTC](https://www.ruby-forum.com/t/weird-variable-scope-behaviour/115276/1 "2007-09-23T00:36:19Z")
I just wrote some code that shouldn’t have worked, in my estimation, but it did, anyway. While this was a pleasant surprise, I prefer to understand why things don’t work than to wonder why they did work… ``` What was happening is this situation, here: ``` if false variable = true end if variable #do something end ``` To my surprise, this is okay! Even though the code in the first ``` if-clause doesn’t get run, the variable in the clause gets created, anyway… Now, I’m pretty sure this is expected behaviour. What I’m wondering is how people feel about this. This behaviour makes me feel uneasy. If I’m using a variable that hasn’t been deliberately created then I’d rather have the interpreter complain that I haven’t created the variable, as planned, than to be confused as to why my variable is nil. I’m very interested to hear other opinions on the subect. Anyone care to comment? Thank you… ---
**Author:** ![maz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@maz](https://www.ruby-forum.com/u/maz)\ **Post date:** [September 23, 2007, 1:20am UTC](https://www.ruby-forum.com/t/weird-variable-scope-behaviour/115276/2 "2007-09-23T01:20:54Z")
Just Another Victim wrote: > if false > variable = true > end > > if variable > #do something > end > > ``` > To my surprise, this is okay! > > ``` What do you mean by “okay”? Does the following not work as you would expect: if false x = 10 end if x puts “yep” else puts “nope” end Also, see here: [http://www.ruby-forum.com/topic/124638#new](http://www.ruby-forum.com/topic/124638#new) ---
**Author:** ![maz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@maz](https://www.ruby-forum.com/u/maz)\ **Post date:** [September 23, 2007, 1:23am UTC](https://www.ruby-forum.com/t/weird-variable-scope-behaviour/115276/3 "2007-09-23T01:23:20Z")
7stud – wrote: > What do you mean by “okay”? Ok, I see: > This behaviour makes me feel uneasy. If > I’m > using a variable that hasn’t been deliberately created then I’d rather > have > the interpreter complain that I haven’t created the variable, as > planned, > than to be confused as to why my variable is nil. ---
**Author:** ![maz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@maz](https://www.ruby-forum.com/u/maz)\ **Post date:** [September 23, 2007, 1:36am UTC](https://www.ruby-forum.com/t/weird-variable-scope-behaviour/115276/4 "2007-09-23T01:36:01Z")
7stud – wrote: > Does the following not work as you would > expect: > > if false > x = 10 > end > > if x > puts “yep” > else > puts “nope” > end Ah. I see what you are concerned about: if y puts “yep” else puts “nope” end undefined local variable or method `y’ for main:Object (NameError) ---
**Author:** ![maz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@maz](https://www.ruby-forum.com/u/maz)\ **Post date:** [September 23, 2007, 5:20am UTC](https://www.ruby-forum.com/t/weird-variable-scope-behaviour/115276/5 "2007-09-23T05:20:39Z")
On Sep 22, 4:32 pm, “Just Another Victim of the Ambient M.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > if variable > than to be confused as to why my variable is nil. > I’m very interested to hear other opinions on the subect. Anyone care > to comment? > Thank you… I understand the behavior, and I’ve learned to live with it. But (as I’ve noted on numerous occassions) I really don’t like the reverse side effect, that you can’t write: p foo if foo=true even though you can write: if foo=true then p foo; end That two statements that are semantically identical should result in different behavior when foo has not previously been assigned a value is an unfortunate side effect/tradeoff of the implementation details and choices. I accept it in the same way I accept that arrays and hashes have, in some cases, traded purity for speed. It ain’t perfect, but it’s what we got. ---
**Author:** ![maz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@maz](https://www.ruby-forum.com/u/maz)\ **Post date:** [September 24, 2007, 4:10am UTC](https://www.ruby-forum.com/t/weird-variable-scope-behaviour/115276/6 "2007-09-24T04:10:32Z")
“Phrogz” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote in message news:removed\_email\_address@domain.invalid… > is an unfortunate side effect/tradeoff of the implementation details > and choices. > > I accept it in the same way I accept that arrays and hashes have, in > some cases, traded purity for speed. It ain’t perfect, but it’s what > we got. ``` I'm interested in to what you're referring, here. How was purity of ``` arrays and hashes compromised for speed? Thank you… ---
**Author:** ![maz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@maz](https://www.ruby-forum.com/u/maz)\ **Post date:** [September 24, 2007, 5:02am UTC](https://www.ruby-forum.com/t/weird-variable-scope-behaviour/115276/7 "2007-09-24T05:02:36Z")
On Sep 23, 8:05 pm, “Just Another Victim of the Ambient M.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > “Phrogz” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote in message > > > I accept it in the same way I accept that arrays and hashes have, in > > some cases, traded purity for speed. It ain’t perfect, but it’s what > > we got. > > ``` > I'm interested in to what you're referring, here. How was purity of > > ``` > > arrays and hashes compromised for speed? Things like the fact that Hash and Array literals don’t call their #initialize method, or that all Array methods that fetch values from the array don’t fall back on a single method that one can intercept or override. ---
**Author:** ![maz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e9c0ed/32.png) [@maz](https://www.ruby-forum.com/u/maz)\ **Post date:** [September 24, 2007, 4:05am UTC](https://www.ruby-forum.com/t/weird-variable-scope-behaviour/115276/8 "2007-09-24T04:05:32Z")
“7stud --” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote in message news:removed\_email\_address@domain.invalid… > > ``` > > puts "yep" > > > > ``` > > puts “nope” > end > > undefined local variable or method `y’ for main:Object (NameError) ``` I'm not sure, exactly, what I'm concerned about but I can give you ``` some clues. It’s a little weird that the above code with variable y results in a name error but the previous example with variable x simply results in a nil object reference. It seems as if they should both result in a nil object reference or they should both result in a name error, rather than being inconsistent with each other. The most pragmatic example of a problem, that I can think of, is a situation where you have a bug that’s immediately caused by a variable that’s unexpectedly nil. Now, you have to trace back the life of the variable, which can traverse many different scopes, to hopefully discover that there was an execution path that didn’t initialize the variable. Instead, wouldn’t it have been nice if the interpreter simply told you, at the variable’s first use, that it didn’t exist 'cause it wasn’t initialized? Now that I put it this way, I think I see how its current behaviour is an implementation detail, done for increasing speed, leaking through the interface…