# Create local variable in Binding after it's creation **URL:** \ **Category:** Ruby\ **Created:** [November 12, 2006, 3:07pm UTC](https://www.ruby-forum.com/t/create-local-variable-in-binding-after-its-creation/75702 "2006-11-12T15:07:54Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![caefer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/e36b37/32.png) [@caefer](https://www.ruby-forum.com/u/caefer)\ **Post date:** [November 12, 2006, 3:07pm UTC](https://www.ruby-forum.com/t/create-local-variable-in-binding-after-its-creation/75702/1 "2006-11-12T15:07:54Z")
Hi, Is it possible to create a new local variable in a binding after it’s creation? Specifically, what I’d like to do: l = lambda { puts a } # ‘a’ not defined at this point. eval(‘a = 7’, l.binding) # Hope to create a in l’s binding l.call # Hope to get ‘7’ - but that produces: Apparently, ‘a’ gets created in the scope from where ‘eval’ was called and not in ‘l’’'s binding. Any suggestions would be most welcome. best regards Christian S. ---
**Author:** ![caefer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/e36b37/32.png) [@caefer](https://www.ruby-forum.com/u/caefer)\ **Post date:** [November 12, 2006, 3:19pm UTC](https://www.ruby-forum.com/t/create-local-variable-in-binding-after-its-creation/75702/2 "2006-11-12T15:19:55Z")
On Sun, Nov 12, 2006 at 11:06:44PM +0900, Christian S. wrote: > Is it possible to create a new local variable in a binding after it’s creation? You can create it, but you won’t be able to use it directly. > Specifically, what I’d like to do: > > l = lambda { puts a } # ‘a’ not defined at this point. > eval(‘a = 7’, l.binding) # Hope to create a in l’s binding > l.call # Hope to get ‘7’ l = lambda{ eval ‘a’ } eval(‘a = 7’, l.binding) l.call # =\> 7 eval(‘a’) # =\> 7 If you try to use ‘a’ before the parser sees ‘a = …’, it will be considered a method call, and you’ll get a NameError even if you give it a value afterwards/in eval. BTW. this is changing in 1.9. ---
**Author:** ![caefer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/e36b37/32.png) [@caefer](https://www.ruby-forum.com/u/caefer)\ **Post date:** [November 12, 2006, 3:28pm UTC](https://www.ruby-forum.com/t/create-local-variable-in-binding-after-its-creation/75702/3 "2006-11-12T15:28:01Z")
Søndag 12 november 2006 15:18 skrev Mauricio F.: > If you try to use ‘a’ before the parser sees ‘a = …’, it will be considered > a method call, and you’ll get a NameError even if you give it a value > afterwards/in eval. Ah, I see. Thanks. > BTW. this is changing in 1.9. In what way? My example seems to work the same way with ruby-1.9… best regards Christian S. ---
**Author:** ![caefer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/e36b37/32.png) [@caefer](https://www.ruby-forum.com/u/caefer)\ **Post date:** [November 12, 2006, 4:24pm UTC](https://www.ruby-forum.com/t/create-local-variable-in-binding-after-its-creation/75702/4 "2006-11-12T16:24:08Z")
On 11/12/06, Mauricio F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > eval(‘a = 7’, l.binding) # Hope to create a in l’s binding > > afterwards/in eval. > > BTW. this is changing in 1.9. > > – > Mauricio F. - [http://eigenclass.org](http://eigenclass.org) - singular Ruby > > I do not want to argue with Mauricio, I know when I am outclassed(1), but > maybe one should suggest a different approach to OP. > Can you use instant variables, or will that be impacting elsewhere p = Proc.new { puts @a } @a= Guess what? p.call And yes Mauricio can you give a pointer to the new behavior please, thx. Cheers Robert (1) Well I do not, but that remains between us 😉 – The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man. - George Bernard Shaw ---
**Author:** ![caefer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/e36b37/32.png) [@caefer](https://www.ruby-forum.com/u/caefer)\ **Post date:** [November 12, 2006, 4:28pm UTC](https://www.ruby-forum.com/t/create-local-variable-in-binding-after-its-creation/75702/5 "2006-11-12T16:28:09Z")
On Sun, Nov 12, 2006 at 11:27:07PM +0900, Christian S. wrote: > In what way? My example seems to work the same way with ruby-1.9… Both eval(“a = 7”) eval(“a”) and eval(“a = 7”, binding) eval(“a”) will raise a NameError in the future, so you’ll have to do binding = binding # heh eval(“a = 7”, binding) eval(“a”, binding) [ruby-core:09388] This can be seen as a step towards less inclusive closures and lambda lifting. ---
**Author:** ![caefer](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/e36b37/32.png) [@caefer](https://www.ruby-forum.com/u/caefer)\ **Post date:** [November 12, 2006, 5:04pm UTC](https://www.ruby-forum.com/t/create-local-variable-in-binding-after-its-creation/75702/6 "2006-11-12T17:04:13Z")
On Mon, Nov 13, 2006 at 12:22:26AM +0900, Robert D. wrote: > > If you try to use ‘a’ before the parser sees ‘a = …’, it will be > > considered a method call, and you’ll get a NameError even if you give it a > > value afterwards/in eval. > > > > BTW. this is changing in 1.9. (Just to be clear, “this” == semantics of eval(“local\_var”)). > And yes Mauricio can you give a pointer to the new behavior please, thx. [ruby-core:09388] I’ll be glad to see that happen; it’s something I’ve been wanting for some time. I became concerned about closures being “too wide” by the end of 2003/early 2004 and was close to writing a RCR. ([http://thekode.net/misc/survey.txt](http://thekode.net/misc/survey.txt) — note: I’m not collecting responses anymore 🙂 [ruby-core:09388] can be interpreted as a step in that direction. PS: your email made me think of the zero derivation of eigenclass and “verbing” it in sentences like “I want to eigenclass myself” or “eigenclassing oneself demands constant effort” which could be the first use ever with the obvious newly-coined? acception 🙂