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.
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, [email protected] [email protected] 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.
On 11/4/06, [email protected] [email protected] 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 | [email protected]
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 | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com | [4] 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.
On 11/4/06, Devin M. [email protected] 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.
$ 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
On 11/4/06, David V. [email protected] 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.
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.