value_object.rb

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db_adapters.cr state_machine.cr value_object.cr visitor.cr db_adapters.rb log_decorator.rb validation.rb value_object.rb visitor.rb

value_object.rb
¶

The whole idea of this is to have barebones “value object factory” that creates new classes for the given attribute names.
¶

This method will be invoked for a class object. For example, let’s say a Money class. It’ll add an initialize for the class with the given arguments as parameters, and it’ll set the instance variable with the same name for each attribute.
```
def vo_initialize(attributes)
  define_method("initialize") do |values|
    attributes.zip(values).each do |attribute, value|
      instance_variable_set("@#{attribute}", value)
    end
  end
end
```

This other method will add reader methods that return the value of each attribute

def vo_readers(attributes)
  attributes.each do |attribute|
    define_method(attribute) do
      instance_variable_get("@#{attribute}")
    end
  end
end

¶

Finally we have the factory, this returns a new instance of Class (so, a class!). When we pass a block to Class.new, it gets executed in the context of the newly created class
```
def value_object(*attributes)
  Class.new do
    vo_initialize(attributes)
    vo_readers(attributes)
  end
end
```

Tada!

Money = value_object("currency", "amount")