问题
Couldn't explain my question succinctly enough in the title, so I'm putting it here. It will actually be easier to show the code before asking my question:
array1 = []
array2 = [1,2,3]
array1 = array2
#=> array1 = [1,2,3]
array2.clear
#=> array1 = []
#=> array2 = []
Why does using the .clear method on the second array also clear what is in the first array? I guess what I'm asking is, once we set array1 = array2, why is array1 affected by the .clear we apply to array2? It seems that array1 = array2 will hold true for the duration of my script, is this right?
In order for array1 to remain unchanged once I do array2.clear, would I need to implement array1 = array2 a different way, such as using a for loop and .unshifting elements from array2 and .pushing them over to array1?
回答1:
When you do
array1 = array2
array1 and array2 reference to the same Array object now. So any modifications you make to either will affect to the other.
array1.object_id
# => 2476740
array2.object_id
# => 2476740
See? They have the same object_id.
If this behavior is not what you expected, try
array1 = array2.dup
or
array1 = array2.clone
回答2:
You may be confused because with integers it seems like it works differently:
a = 6 # puts "6" into a memory location, and point "a" to it
b = a # points "b" to the same memory location as "a"
b = 7 # puts "7" into a memory location, and point "b" to it.
puts a # 6
puts b # 7
Note that with the = you are telling the variable to point to an object at a certain memory address. Contrast this with your question:
array1 = [] # put empty array in memory and points array1 to it
array2 = [1,2,3] # put [1,2,3] array into memory and point array2 to it
array1 = array2 # make array2 point to same location as array1
#=> array1 = [1,2,3]
array2.clear # tell ruby to clear the memory location pointed to by array2 (uh oh, array1 pointing to same place!)
来源：https://stackoverflow.com/questions/30315197/using-clear-method-in-ruby