Example where data structure is hidden

DependOnBehaviourNotData-p4.md

# consider this person class:

class Person
	attr_reader :age, :weight
	def initialize(data)
		@age = data[0]
    @weight = data[1]
	end
end

p = Person.new([35, 150])

# now let's access this person's age.
# notice now we don't care whether 
# the underlying data structure is a hash,
# or is an array. All we know (and care) is that
# if we send an "age" message to the p Person
# then we will get that Person's age.

age = p.age

# same goes for her weight
weight = p.weight

p1 = Person.new([50, 110])
p1_age = p1.age
p1_weight = p1.weight