T
T. Onoma
is there anyway, anyway at all, ugly hacks accepted, of doing inplace
assignment in Ruby?
assignment in Ruby?
H
Hal Fulton
T. Onoma said:
Not sure what you mean, can you give an example from
some other language? Or just explain?
Hal
T
T. Onoma
Sure,
q = 1
p q.__id__ # => 3
q = 2
p q.__id__ # => 5 (want this to still be 3)
In other words I want to change what q "contains" rather then alter its
reference. With an array for example you can do that with #replace. In
particular I'm interesed in doing this with constants.
N
nobu.nokada
Hi,
At Sun, 14 Dec 2003 15:14:44 +0900,
Array#replace isn't concerned with constants.
A = [1]
A.replace([2])
p A[0] # => 2
At Sun, 14 Dec 2003 15:14:44 +0900,
T. Onoma said:
Array#replace isn't concerned with constants.
A = [1]
A.replace([2])
p A[0] # => 2
H
Hal Fulton
T. Onoma said:
OK, I thought that was what you meant.
String also has a replace. But there's no general Object#replace.
My impression is that this in impossible in general, and for
immediate values such as Fixnums, "even more impossible."
The idea of doing this with a constant is scary to me. It's bad
enough that a constant String or Array can be changed. And it's
even scarier to think of doing that with something like a
Fixnum.
What's the situation where you'd want to do this?
Hal
G
Gavin Sinclair
For "constants" I presume you mean "integers" here? (Constants can be
of any class, and simply mean a variable that begins with a capital
letter, and which are thinly guarded against reassignment.)
You certainly can't do what you're asking in Ruby. Fixnum values are
hardcoded objects for performance reasons.
Fixnums aside, there's nothing you can do to change the behaviour of
"=".
Gavin
H
Hal Fulton
Thanks for pointing this out. I don't think I ever noticed that.
Should this give an error?
Hal
N
nobu.nokada
Hi,
At Sun, 14 Dec 2003 15:50:54 +0900,
No. A constant in Ruby is a name which can point to only
particular object. Nothing related to the container's
contents.
At Sun, 14 Dec 2003 15:50:54 +0900,
Hal said:
No. A constant in Ruby is a name which can point to only
particular object. Nothing related to the container's
contents.
T
T. Onoma
Well, the reason its a constant is b/c its a class. It's funny how things come
up. I only recently learned that when you modify a class, all previously
defined objects of that class are effected. But what if you want to pull the
entire "rug out", so to speak, and replace a class with a "duck similiar"
class?
Okay, so it's a bit crazy. But I actually came across a use for this. Luckly
my situation is specialized --I am replacing the class with a subclass of it,
so I discovered that I could just do this:
class MyClass < MyClass
(and now that I think about it I can probably do this for any calss) it seems
to work fine.
but now i'm running into an disturbing problem. next post...
G
Gavin Sinclair
That's what #freeze is for.
Gavin
M
Mauricio Fernández
Don't you like open classes? ;-)
--
_ _
| |__ __ _| |_ ___ _ __ ___ __ _ _ __
| '_ \ / _` | __/ __| '_ ` _ \ / _` | '_ \
| |_) | (_| | |_\__ \ | | | | | (_| | | | |
|_.__/ \__,_|\__|___/_| |_| |_|\__,_|_| |_|
Running Debian GNU/Linux Sid (unstable)
batsman dot geo at yahoo dot com
/*
* Please skip to the bottom of this file if you ate lunch recently
* -- Alan
*/
-- from Linux kernel pre-2.1.91-1
D
Dan Doel
Mauricio said:
I think he's more afraid of:
1 = 2
p 1 + 1 # => 4
- Dan
H
Hal Fulton
Actually, I completely misread your example. I already understood this
phenomenon.
I thought that the assignment was silently discarded, i.e., I read this
as:
A = [1]
A.replace([2])
p A[0] # => 1
Sorry for being stupid.
Hal
G
gabriele renzi
il Sun, 14 Dec 2003 15:50:54 +0900, Hal Fulton
every 'changeable' object, such has String, Hash, Array etc works this
way. The point is that the object refernce is constant, not the
object.
IMO this is a work for freeze() , if you really want an error
every 'changeable' object, such has String, Hash, Array etc works this
way. The point is that the object refernce is constant, not the
object.
IMO this is a work for freeze() , if you really want an error
H
Hal Fulton
gabriele said:
Thank you. Yes, I knew this already. My brain was not working properly.
Thanks,
Hal
R
Robert Klemme
T. Onoma said:
You want to change the state of the instance at hand and don't want to
change its identity. It depends on the type of instance at hand whether
you can achieve your goal: it doesn't work for integers, but you can
change a String (which also works for constants):
irb(main):016:0> s = "foo"
=> "foo"
irb(main):017:0> s.id
=> 135086644
irb(main):018:0> s = "bar"
=> "bar"
irb(main):019:0> s.id
=> 135071956
irb(main):020:0> s.replace "foo"
=> "foo"
irb(main):021:0> s.id
=> 135071956
irb(main):022:0>
There is no general solution to what you want. Personally I never needed
this feature. Normally you can solve this with proper nesting.
Keep in mind that the constness of constants is all constants are about.
So changing them is generally not a good idea if it's a simple type like
String or Integer.
Regards
robert