# Redefining a class **URL:** \ **Category:** Ruby\ **Created:** [November 7, 2006, 11:01am UTC](https://www.ruby-forum.com/t/redefining-a-class/74902 "2006-11-07T11:01:02Z")\ **Posts on this page:** 9\ **Page:** 1

**Author:** ![flatekmonkey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e8c25b/32.png) [@flatekmonkey](https://www.ruby-forum.com/u/flatekmonkey)\ **Post date:** [November 7, 2006, 11:01am UTC](https://www.ruby-forum.com/t/redefining-a-class/74902/1 "2006-11-07T11:01:02Z")

Hi all Recently we had a thread where we talked about redefining a class. The usefuleness of that did not come into my mind before. Does somebody know a way to redefine a class (without the "already initialized constant " warning)? And if there is none, which I suspect, might it not be nice to have one? Cheers Robert – 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 ---

On Sat, 4 Nov 2006, Robert D. wrote: > Hi all > > Recently we had a thread where we talked about redefining a class. > The usefuleness of that did not come into my mind before. > > Does somebody know a way to redefine a class (without the "already > initialized constant " warning)? > And if there is none, which I suspect, might it not be nice to have one? c = Class.new{ def initialize @x = ‘foo’ end } o = c.new c = Class.new{ def initialize @x = ‘bar’ end } o = c.new 😉 -a ---

On 11/4/06, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > And if there is none, which I suspect, might it not be nice to have one? > > def initialize > > my religion is very simple. my religion is kindness. – the dalai lama Actually I am very disappointed that you cannot read my mind Ara 😉 it would be quite antipols to use not constant classnames (wouldn’t be there some warnings too BTW?) class C… C=Class.new… works fine save for the warning I would like to get around Here go some ideas: (1) ruby does not insult you for constant redefinition if you assign a reference to Class (arrrghh bad dangerous) (2) allow an explicit syntax for redefining a class (2.a) class A \< B _always_ redefines the class Pro: Some Gurus expect this behavior anyway 🙂 Cons: Quite implicit (2.b) new class A Pro: Quite POLS and readable Cons: “new” overloaded maybe use “redefine class A” (3) some meta thingies (3.a) const\_set does not warn anymore (3.b) Matz gives us a const\_undefine for Christmas 😉 Ok what you think? Robert – 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 ---

On 11/4/06, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > > > > > > > > ``` > > > def initialize > > > > > > ``` > > > > > > o = c.new > > > (Specifically, he said “Policy of least surprise is _my_ least > > > surprise”. I think it was at RubyConf 2002.) And you think we ought let him get away with that 😉 I wouldn’t expect a warning just from assigning a class object to a > > (1) ruby does not insult you for constant redefinition if you assign a > > > Quite POLS and readable > > Cons: “new” overloaded maybe use “redefine class A” > > (3) some meta thingies > > (3.a) const\_set does not warn anymore > > (3.b) Matz gives us a const\_undefine for Christmas 😉 > > > > Ok what you think? > > Basically I think that if you find yourself in urgent need of defining > a new class using the same constant as one you’ve already defined, you > need to review your application design 🙂 Honestly I do not know, probably yes, because it did never even occur to me. OTH you can already redefine classes as Ara showed above, only that one will use a different idiom. I can also redefine classes by hiding classes inside Modules e.g. than one does not know if it is done on purpose or not. Imagine the semantic power of " redefine class ::String " although that kind of code might disgust you (it disgusts me!) it tells us that the author knows what he does, quite a feature, no? The warning is probably > enough of a slap on the wrist to remind you of this. > > I do, however, think that (3.a) might be a good idea. I’m not sure, > though. Thanks that’s more than I expected 😉 David > – > David A. Black | removed\_email\_address@domain.invalid > Author of “Ruby for Rails” [1] | Ruby/Rails training & consultancy [3] > DABlog (DAB’s Weblog) [2] | Co-director, Ruby Central, Inc. [4] > [1] [Ruby for Rails](http://www.manning.com/black) | [3] [http://www.rubypowerandlight.com](http://www.rubypowerandlight.com) > [2] [http://dablog.rubypal.com](http://dablog.rubypal.com) | [4] [http://www.rubycentral.org](http://www.rubycentral.org) Robert – 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 ---

On 11/4/06, Devin M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Devin How could I have missed that one!!! Thx. Well it is not perfect but I think it gets the job done #!/usr/local/bin/ruby def redefine\_class name, base=Object, &definition Object.send :remove\_const, name.to\_s rescue nil cls = Object.const\_set name.to\_s, Class.new( base ) cls.class\_eval &definition if definition end class A end puts A.object\_id redefine\_class A puts A.object\_id redefine\_class A do def greet; puts “hi” end end A.new.greet ## Useless code, I love it 😉 Robert 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 ---

## $ ri remove\_const ---------------------------------------------------- Module#remove\_const remove\_const(sym) =\> obj ``` Removes the definition of the given constant, returning that constant's value. Predefined classes and singleton objects (such ``` as _true_) cannot be removed. For a more thorough answer, read the Rails reloading code. Devin ---

Hi – On Sun, 5 Nov 2006, Robert D. wrote: > > > initialized constant " warning)? > > > c = Class.new{ > > > be quite antipols to use > > > not constant classnames (wouldn’t be there some warnings too BTW?) Don’t forget that several years ago, Matz deprecated POLS 🙂 (Specifically, he said “Policy of least surprise is _my_ least surprise”. I think it was at RubyConf 2002.) I wouldn’t expect a warning just from assigning a class object to a variable. > (2) allow an explicit syntax for redefining a class > (2.a) class A \< B _always_ redefines the class Pro: Some Gurus expect > this behavior anyway 🙂 Not a good idea. The inheritance should be a no-op if it already exists, and an error if it’s a different class. The expression “A \< B” does not in any way imply that A should be undefined. You’d end up seeing: class C \< Object just to trigger a redefinition. It’s piggy-backing a behavior (constant redefinition) on a completely unrelated construct. > Cons: Quite implicit And arbitrary. > (2.b) new class A Pro: > Quite POLS and readable > Cons: “new” overloaded maybe use “redefine class A” > (3) some meta thingies > (3.a) const\_set does not warn anymore > (3.b) Matz gives us a const\_undefine for Christmas 😉 > > Ok what you think? Basically I think that if you find yourself in urgent need of defining a new class using the same constant as one you’ve already defined, you need to review your application design 🙂 The warning is probably enough of a slap on the wrist to remind you of this. I do, however, think that (3.a) might be a good idea. I’m not sure, though. David ---

**Author:** ![flatekmonkey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e8c25b/32.png) [@flatekmonkey](https://www.ruby-forum.com/u/flatekmonkey)\ **Post date:** [November 7, 2006, 11:03am UTC](https://www.ruby-forum.com/t/redefining-a-class/74902/8 "2006-11-07T11:03:18Z")

On 11/4/06, David V. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > objects, including classes you intend to redefine. > Actually clear like water, I was wrting stupid things, it is only > anticonventional . > I have problems defending I feature I dislike and yet feel it should be > here > because… (On the possibility > of redefining classes -outside- your code I shan’t speak, because I’d > have to get vulgar. Prolific namespace clobbering already gets on my > nerves, and I wish there was a way to localise such changes requiring a > module causes. /me gets off soapbox.) And I sure as hell would find it > surprising if suddenly a hash keyed by what I thought were constant > objects started breaking. … there is some truth(1) in what you are saying. No doubt one of the reasions why remove\_const is private. David V. > Robert ## (1) although strictly speaking there is no such thing I mean “POV I share to some degrees” 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:** ![flatekmonkey](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/e8c25b/32.png) [@flatekmonkey](https://www.ruby-forum.com/u/flatekmonkey)\ **Post date:** [November 7, 2006, 11:02am UTC](https://www.ruby-forum.com/t/redefining-a-class/74902/9 "2006-11-07T11:02:16Z")

Robert D. wrote: > Actually I am very disappointed that you cannot read my mind Ara 😉 it > would > be quite antipols to use > not constant classnames (wouldn’t be there some warnings too BTW?) If you redefine the class at times, it’s hardly constant. Personally, I think it’s cleaner to use non-constant names for… well… nonconstant objects, including classes you intend to redefine. (On the possibility of redefining classes -outside- your code I shan’t speak, because I’d have to get vulgar. Prolific namespace clobbering already gets on my nerves, and I wish there was a way to localise such changes requiring a module causes. /me gets off soapbox.) And I sure as hell would find it surprising if suddenly a hash keyed by what I thought were constant objects started breaking. David V.