Hi
Can someone explain to me why is this happening ?
matrix1 = ["One","Two","Three"]
=> ["One", "Two", "Three"]
matrix2 = matrix1
=> ["One", "Two", "Three"]
matrix2.shift
=> "One"
matrix2
=> ["Two", "Three"]
matrix1
=> ["Two", "Three"]
According to my logic, when I do matrix2.shift, it should have nothing
to do with matrix1. Why's this one shifted as well ?
--
Posted via http://www.ruby-forum.com/\.
Alle Friday 05 December 2008, Hamza Haiken ha scritto:
Hi
Can someone explain to me why is this happening ?
>> matrix1 = ["One","Two","Three"]
=> ["One", "Two", "Three"]
>> matrix2 = matrix1
=> ["One", "Two", "Three"]
>> matrix2.shift
=> "One"
>> matrix2
=> ["Two", "Three"]
>> matrix1
=> ["Two", "Three"]
According to my logic, when I do matrix2.shift, it should have nothing
to do with matrix1. Why's this one shifted as well ?
Because matrix1 and matrix2 are only different names used to refer to the same
thing, as you can see by checking the values returned by matrix1.object_id and
matrix2.object_id. If you want the two variables to contain different objects,
you need to write
matrix2 = matrix1.dup
This will set the contents of matrix2 to a duplicate of matrix1, so that
changing one won't change the other. Note, however, that this is only a
shallow copy, that is: the array itself is duplicated, but its contents
aren't. This means that any method which changes one of the contained strings
in-place will affect both array. For example:
matrix2 = matrix1.dup
matrix1[0].sub!('O','o')
p matrix1
#=> ["one", "Two", "Three"]
p matrix2
#=> ["one", "Two", "Three"]
If you also need to be sure that the arrays contain different objects, you
need to do a deep copy, which can be achieved using marshal:
matrix2 = Marshal.load(Marshal.dump(matrix1))
I hope this helps
Stefano
# Can someone explain to me why is this happening ?
here matrix1 holds a ptr/reference to the array object
# >> matrix1 = ["One","Two","Three"]
# => ["One", "Two", "Three"]
here the reference is also copied to matrix2
# >> matrix2 = matrix1
# => ["One", "Two", "Three"]
From: Hamza Haiken [mailto:tenkage@gmail.com]
x = [42] makes x refer to the ArrayObject
y = x makes y refer to the *same* object, see for yourself
irb(main):001:0> x=[42]
=> [42]
irb(main):002:0> p x.object_id
77740410
=> 77740410
irb(main):003:0> y = x
=> [42]
irb(main):004:0> p y.object_id
77740410
=> 77740410
Now if you do this
irb(main):005:0> x << 42
=> [42, 42]
guess what y will refer to, still the same object, that happens to
have been altered
irb(main):006:0> y
=> [42, 42]
If you want y to refer to a different object you can do this
irb(main):001:0> x = [42]
=> [42]
irb(main):002:0> y = x.dup
=> [42]
irb(main):003:0> p [x.object_id, y.object_id]
[77455250, 77432630]
=> [77455250, 77432630]
irb(main):004:0> x << 42
=> [42, 42]
irb(main):005:0> p [x, y]
[[42, 42], [42]]
=> [[42, 42], [42]]
HTH
R.
On Fri, Dec 5, 2008 at 10:20 AM, Hamza Haiken <tenkage@gmail.com> wrote:
Hi
Can someone explain to me why is this happening ?
--
Ne baisse jamais la tête, tu ne verrais plus les étoiles.
Robert Dober 