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Class methods are used when a method needs to have functionality but it may not be tied to a specific instance of a class. The extend keyword in Ruby will mix behavior in to a class rather than instances of a class.
Code Samples
We've created a tracking module that creats an instances of something, pushes it on to an instances
array, and then can find it in said array.
module Tracking
def create(name)
object = new(name)
instances.push(object)
return object
end
def instances
@instances ||= []
end
def find(name)
instances.find do |instance|
instance.name == name
end
end
end
From there, when we use the extend
keyword, these methods will apply at the class level and not the instance level.
class Customer
extend Tracking
attr_accessor :name
def initialize(name)
@name = name
end
def to_s
"[#{@name}]"
end
end
Those methods now run at the class level and return instances of the class we just created:
puts "Customer.instances: %s" % Customer.instances.inspect
Output:
Customer.instances: []
Input:
puts "Customer.create: %s" % Customer.create("Jason")
Output:
Customer.create: [Jason]
Input:
puts "Customer.create: %s" % Customer.create("Kenneth")
Output:
Customer.create: [Kenneth]
Input:
puts "Customer.instances: %s" % Customer.instances.inspect
Output:
Customer.instances: [#<Customer:0x007f2b23eabc08 @name="Jason">, #<Customer:0x007f2b23eaba
f0 @name="Kenneth">]
Output:
puts "Customer.find('Jason'): %s" % Customer.find("Jason")
Output:
Customer.find('Jason'): [Jason]
Input:
puts "Customer.find('Mike'): %s" % Customer.find("Mike")
Output:
Customer.find('Mike'):
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