[Ruby] Object assignment and pointers
- by Jergason
I am a little confused about object assignment and pointers in Ruby, and coded up this snippet to test my assumptions.
class Foo
attr_accessor :one, :two
def initialize(one, two)
@one = one
@two = two
end
end
bar = Foo.new(1, 2)
beans = bar
puts bar
puts beans
beans.one = 2
puts bar
puts beans
puts beans.one
puts bar.one
I had assumed that when I assigned bar to beans, it would create a copy of the object, and modifying one would not affect the other. Alas, the output shows otherwise.
^_^[jergason:~]$ ruby test.rb
#<Foo:0x100155c60>
#<Foo:0x100155c60>
#<Foo:0x100155c60>
#<Foo:0x100155c60>
2
2
I believe that the numbers have something to do with the address of the object, and they are the same for both beans and bar, and when I modify beans, bar gets changed as well, which is not what I had expected. It appears that I am only creating a pointer to the object, not a copy of it. What do I need to do to copy the object on assignment, instead of creating a pointer?
Tests with the Array class shows some strange behavior as well.
foo = [0, 1, 2, 3, 4, 5]
baz = foo
puts "foo is #{foo}"
puts "baz is #{baz}"
foo.pop
puts "foo is #{foo}"
puts "baz is #{baz}"
foo += ["a hill of beans is a wonderful thing"]
puts "foo is #{foo}"
puts "baz is #{baz}"
This produces the following wonky output:
foo is 012345
baz is 012345
foo is 01234
baz is 01234
foo is 01234a hill of beans is a wonderful thing
baz is 01234
This blows my mind. Calling pop on foo affects baz as well, so it isn't a copy, but concatenating something onto foo only affects foo, and not baz. So when am I dealing with the original object, and when am I dealing with a copy? In my own classes, how can I make sure that assignment copies, and doesn't make pointers? Help this confused guy out.
