Define Method

We use define method to create a method on the fly given a string as a name.

class A
define_method :c do
puts "Hey!"
end
end
A.new.b
A.new.c(1,2)

Exercise - Green Hamsters

Hamsters come in red, green, blue and orange.

A hamster class looks like this:

class Hamster
attr_accessor :colour
end

for now we'll just assume that only these colours are allowed.

Given an instance of hamster, I would like to be able to call something like:

hammy = Hamster.new
hammy.colour = :red
hammy.is_red?

and have it return true or false

Bonus marks

Rather than defining a limited set of methods in advance, use method_missing to catch when a method is not defined, then define it on the fly. If I call is_taupe? method_missing should catch that, define a Hanster#is_taupe? method, then call it.

Exercise - drying up code

The following real code is full of duplication. How might you use define_method to dry it up?

class Widget
def product
product = Product.find_by_slug(object_slug)
if !product
product = Product.first
end
product
end
def poem
poem = Poem.find_by_slug(object_slug)
if !poem
poem = Poem.first
end
poem
end
end

If you don't want to create a whole Rails instance, you can use a simple scaffold like this:

class Product
class << self
def find_by_slug
return "success"
end
end
end
class Poem < Product; end

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