Comments on: Ruby Scoping Bug?

By: Exeplealarash

Exeplealarash — Sat, 31 Oct 2009 07:06:41 +0000

Other variant is possible also

By: Radarek

Radarek — Fri, 30 Jan 2009 17:22:35 +0000

“When lexer encounters local variable assignment (a=, a||=) within the scope (e.g. method body; if-then-else blocks are not new scopes by design), it marks “a” as a local variable and you have no way to call a method “a” then.”

It’s not true. You can always use “()” to make explicit method call.

By: Radarek

Radarek — Fri, 30 Jan 2009 17:09:50 +0000

Guys, everything is expected. If interpreter would decide that given name is local variable or method in runtime it could works even strangely. Consider this example:

http://pastie.org/375282

class Foo
def title
“Oh hai.”
end

def buggy
puts title

if rand(2) == 0
title = ‘Oh noes!’
end

puts title
end
end

Foo.new.buggy

Depending on returned value by rand(2) it would use sometimes variable title and sometimes call a method. It would be very evil. Now you can be sure: it always use local variable (even if it will be set to nil).

Another advantage of that behavior is that you IDE/editor can say during editing that given name is variable or method. Netbeans do that by make bold methods so looking at code you can see it clearly. It’s very important because one of frequent allegations that people saying is that it’s difficult to say looking on source code if something is method or variable, for example:

def foo
# many lines of code
x = a + b # a and b could be variable of method
end

But we can for 100% say if something is method or variable. As far as I know Perl can’t do that (sometimes) and decide it on runtime. We should be thankful for that.

By: cies breijs

cies breijs — Fri, 30 Jan 2009 10:02:06 +0000

anybody tested it with 1.9?

i think this is one of the issues Matz pointed out he wants to get ‘rite’ in 1.9/2.0.

_cies.

By: ste

ste — Thu, 29 Jan 2009 12:07:59 +0000

class Foo
def title
“Oh hai.”
end

def buggy
puts title

if false
title = ‘Oh noes!’
end

puts title()
end
end

Foo.new.buggy

Oh hai.
Oh hai.

Like Oleg said, “if” does not introduce a new scope: at first “title” is resolved to a method invocation, then intepreter sees a variable assignment inside the _current_ scope, so from there on “title” is bound to a local variable. If for some reason you want to have both a variable and a method with the same name in your code, the least you can do is not fooling the interpreter
I think this “bug” is a very small price to pay to have uniform access.

By: Stephen Sykes

Stephen Sykes — Wed, 28 Jan 2009 23:34:39 +0000

Oleg is right, but it may seem surprising.

See here for some more somewhat surprising results: http://pennysmalls.com/2007/10/01/why-ruby-is-not-my-favourite-programming-language/

By: Mirko Froehlich

Mirko Froehlich — Wed, 28 Jan 2009 23:17:01 +0000

Wow, interesting bug! I don’t have an explanation for it either, and was able to reproduce it in both Ruby 1.8.6 and 1.8.7. It’s good to know this issue exists, as I’m sure it could cause some debugging headaches… However, I generally try to avoid naming my local variables the same as my methods, because of the potential for confusion.

By: Oleg Andreev

Oleg Andreev — Wed, 28 Jan 2009 22:48:54 +0000

This is a feature, not a bug. Ruby knows when “a” is a method or a local variable only by lexer heuristics. When lexer encounters local variable assignment (a=, a||=) within the scope (e.g. method body; if-then-else blocks are not new scopes by design), it marks “a” as a local variable and you have no way to call a method “a” then.

Sometimes this funny behavior is useful:
http://oleganza.tumblr.com/post/57906287/ruby-local-variable-semantics

In my practice i have never had a trouble with these semantics: i have small methods, thus little number of local variables, and well-chosen names for everything.