Append Hash to Array - ruby

Question

I have a little problem with this exercise, can you help me? I tried to edit a script, but for each time that I create new instance the last element overwrites the Others (i.e. )
The class must provide a functionality for the combination of consequent blocks: i.e. it must be able to inherit from the previous block the instructions that have not been explicitly defined for the current block.
blocks = []
blocks << Block.new({ X:0, Y:100, Z:20}) # p blocks:({ X:0, Y:100, Z:20})
blocks << Block.new({X:100}, blocks[-1]) #p blocks:({ X:100, Y:100, Z:20},{ X:100, Y:100, Z:20})
blocks << Block.new({Y:0}, blocks[-1]) #p blocks:({ X:100, Y:0, Z:20},{ X:100, Y:0, Z:20},{ X:100, Y:0, Z:20})
My code with problems is:
#!/usr/bin/env ruby
class Block
$instance_2 = true
$instance_3 = true
attr_reader :out
def initialize(out, previous = nil )
#out = update(out, previous)
end # end initialize
def update(actual, previous)
puts "IN UPDATE: box is: #{previous}"
box = previous
if box != nil
puts "IF: changing is: #{actual}"
actual.each do |key, value|
box[key] = value
end
box
else
puts "ELSE"
actual
end # end if
end # end update
def inspect
#out
end
end # end Block
blocks = []
puts "\n#----------------------1 INSTANCE----------------------#"
blocks << Block.new({G: "00", X: 100, Y:100, Z: 100})
puts "\n#----------------------blocks element----------------------#"
p blocks
puts "last block is: #{blocks[-1].out}"
puts "\n#----------------------2 INSTANCE----------------------#" if $instance_2
blocks << Block.new({G: "01"}, blocks[-1].out) if $instance_2
puts "\n#----------------------blocks element----------------------#"if $instance_2
p blocks if $instance_2
puts "last block is: #{blocks[-1].out}"
puts "\n#----------------------3 INSTANCE----------------------#" if $instance_3
blocks << Block.new({G: "02"}, blocks[-1].out) if $instance_3
puts "\n#----------------------blocks element----------------------#" if $instance_3
p blocks if $instance_3
puts "last block is: #{blocks[-1].out}"
puts "\n#----------------------4 INSTANCE----------------------#" if $instance_3
blocks << Block.new({G: "03"}, blocks[-1].out) if $instance_3
puts "\n#----------------------blocks element----------------------#" if $instance_3
p blocks if $instance_3
puts "last block is: #{blocks[-1].out}"

Answer 1

The question is not exactly clear, but if I understand it correctly it is possible to provide a class that may or not accept a previous Block. What do you think of something like that?
#!/usr/bin/env ruby
class Block < Hash
def initialize(h, b=nil)
[:x, :y, :z].each do |s|
# We start by trying to assign the coordinate that is in the
# input hash
if h[s]
self[s] = h[s]
else
# If the coordinate is not in h, we check for it in b, but we have to
# remember that if the block that we are providing in b does not have
# the method :[] or the coordinate is nil we may raise an exception
begin
self[s] = b[s]
raise if not self[s]
rescue
raise(Exception, "Cannot initialize block.")
end
end
end
end
def inspect
"block:(x: #{self[:x]}, y: #{self[:y]}, z: #{self[:z]}"
end
end
# Let's try it!
blocks = []
blocks << Block.new({ x:0, y:100, z:20})
puts blocks
puts
blocks << Block.new({x:100}, blocks[-1])
puts blocks
puts
blocks << Block.new({y:0}, blocks[-1])
puts blocks
puts
With respect to your code
Let's consider only the update method:
def update(actual, previous)
puts "IN UPDATE: box is: #{previous}"
box = previous # ! ! ! ! ! ! ! ! WHOOPS!
if box != nil
puts "IF: changing is: #{actual}"
actual.each do |key, value|
box[key] = value
end
box
else
puts "ELSE"
actual
end # end if
end # end update
the "whoops" line is what is creating you the issue. With that line
you are giving the reference to previous (your object variable actually contains a reference) to the box variable. What you are actually doing, when you perform some action on box, is modifying what is pointed by both variable.
You can test what I'm saying immediately. Try to modify that line in this way:
box = previous.clone if previous
(nil does not have a method #clone that the rationale behind the if). If you run it again you will get a list of blocks that have not being modified. This is not an efficient code tough, and you should really rethink the update method code.