From: "Peña, Botp" <botp@...>
Date: 2008-05-23T19:58:00+09:00
Subject: Re: Prevent ruby constant variables from changing?

From: Robert Dober [mailto:robert.dober@gmail.com] 
#

ff is my limited understanding of ruby.. pardon in advance..

# irb(main):001:0> class A
# irb(main):002:1> end
# => nil

here we defined a class object referenced by a constant A, ruby gives the object a name "A". The name "A" is now set in stone :)
Consider "A" as the name of A, or the name of object named A. ...arggh, this reminds of me something... No worry, it's just a name..  :)

# irb(main):003:0> B = A
# => A

we copy the constant A to constant B. B now points to class pointed by A wc is still named "A". 

# irb(main):004:0> class B
# irb(main):005:1> def a; 42 end
# irb(main):006:1> end
# => nil

we define a method a in class referred by constant B, wc is A, ergo we are reopening A.

# irb(main):007:0> A.new.a
# => 42

ok

# irb(main):008:0> B.name
# => "A"

the (class) object referred to by B is still named "A". Stoned. Even if you remove constant A, B.name will still be "A"

(note, you just operationaly demonstrated what XNoria wrote in prev post :)


# I just feel to think more seriously now never to use "class X" again,
# I want to avoid the very subtle inconsistencies it implies but I
# really hate, that after
# 
# C = Class::new
# C.name equals "C".

ruby's behaviour is to get the class name fr the very first constant it encounters or it is assigned to. yes, by the very fact that _it_ is a constant. sorry, but what could be simpler?  We've assigned it to a constant, and still we expect it to have no name?? But hey, again, it's just a name. maybe what is confusing here is the word "name" itself :)

irb(main):001:0> A=B=C=Class.new
=> C
irb(main):002:0> A.name
=> "C"
irb(main):003:0> B.name
=> "C"
irb(main):004:0> C.name
=> "C"

constant C is not coupled w name "C", see,

irb(main):007:0> Object.send :remove_const, :C
=> C
irb(main):008:0> C.name
NameError: uninitialized constant C
        from (irb):8
        from :0
irb(main):009:0> A.name
=> "C"
irb(main):010:0> B.name
=> "C"


# irb(main):001:0> C = _ = Class::new
# => C
# irb(main):002:0> C.name
# => "C"
#
# but finally
# 
# irb(main):006:0> _ = Class::new
# => #<Class:0xb7d5af90>
# irb(main):007:0> _.name
# => ""

in ruby1.9, this is nil. wc mean, we have no name yet. better than saying my name is empty.


btw, careful w using "_" in irb, since irb uses it :)


# irb(main):008:0> X = _
# => ""

of course, since the last result was ""

# irb(main):009:0> X.name
# NoMethodError: undefined method `name' for "":String
#         from (irb):9
#         from :0
# irb(main):010:0>

as expected


kind regards -botp