This is a contrived example to emulate what is going on in another project. I'm sure I'm just misunderstanding some basic function of classes, but I don't know where to look to find the answer.
If I set an instance variable @empty = [] in the parent class, then I want to use the original instance variable, as well as a variation of the instance variable in a child class, I'm getting an issue where the original instance variable is no longer accessible in its original form.
class Parent
def initialize
@empty = []
end
def fill
@empty << "foo" #interestingly, changing the << to = fixes it, but that's not a possibility on my project
end
end
class Child < Parent
def initialize
super
@should_still_be_empty = @empty #trying to "make a copy" of the original
end
def show_original_variable
@should_still_be_empty
end
end
child = Child.new
child.fill #=> ["foo"], which is what it should return
child.show_original_variable #=> ["foo"], I want it to return []
After playing around a little more, I noticed that this happens within the same classes, as well. Why?
class Child
def initialize
@original_empty = []
@copy_of_empty = @original_empty
end
def fill
@copy_of_empty << "foo"
end
def show_empty
@original_original_variable
end
end
child = Child.new
child.fill #=> ["foo"]
child.show_original_variable #=> ["foo"], but I want it to be empty
You question has nothing in particular to do with classes or inheritance. Rather, it deals with more basic issues related to assignment and mutation.
xs = [11,22,33]
ys = xs # Both variables hold a reference to the same data.
zs = xs.dup # But zs has a copy (at least a shallow copy).
xs << 44 # If we *mutate* xs, ys changes also.
p xs # [11, 22, 33, 44]
p ys # [11, 22, 33, 44]
p zs # [11, 22, 33]
xs = [4,5,6] # If we *assign* to xs, ys won't be affected.
p xs # [4,5,6]
p ys # [11, 22, 33, 44]
The same behaviors would be observed even if the xs array started out empty (as in your code), but it's a little easier to illustrate with data values present.
If you want @should_still_be_empty to have an independent copy of the underlying data values, you need to do something along these lines:
@should_still_be_empty = @empty.dup
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