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One thing that’s really neat about the include method when using a module is that it gives us a way to hook in to that behavior and do something when a module is included in a class. We can use this to further extend the functionality in our modules. For example, when a module is included in a class, we could use that to run methods, write methods, or include other modules.
Code Samples
First, we modify our Fetcher
module to have an included
class method. This method defines an attribute on the class it is included in called fetch_count
.
module Fetcher
def self.included(klass)
attr_accessor :fetch_count
end
The fetch
method is then modified to say how many times the fetch count has occurred. The ||=
operator is called the conditional assignment operator. It conditionally sets the value of @fetch_count
to 0 if we haven't accessed it yet.
def fetch(item)
@fetch_count ||= 0
@fetch_count += 1
puts "[#{@name}, Fetch count: #{@fetch_count}] I'll bring that #{item} right back!"
end
end
class Dog
include Fetcher
def initialize(name)
@name = name
end
end
dog = Dog.new("Fido")
dog.fetch("ball")
dog.fetch("toy")
Now, when we create a new Dog
instance and run the fetch
method, we get the following output:
[Spot, Fetch count: 1] I'll bring that ball right back!
[Spot, Fetch count: 2] I'll bring that toy right back!
This fetch_count
variable is specific to each Dog
instance:
dog2 = Dog.new("Spot")
dog2.fetch("ball")
dog2.fetch("toy")
So running that produces the following output:
[Fido, Fetch count: 1] I'll bring that ball right back!
[Fido, Fetch count: 2] I'll bring that toy right back!
[Spot, Fetch count: 1] I'll bring that ball right back!
[Spot, Fetch count: 2] I'll bring that toy right back!
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