SimpleDelegator

SimpleDelegator is a class in Ruby’s standard library used to create lightweight decorator objects that delegate most method calls to another object. It is part of the Delegator framework, and SimpleDelegator inherits from Delegator to provide a straightforward way to wrap an object while allowing selective augmentation or override of behavior.

How it works: when you initialize a SimpleDelegator with a target object, method calls that are not defined on the wrapper are forwarded to the wrapped object. The delegation mechanism relies on internal access to the wrapped object, typically via the __getobj__ method, which also lets you inspect or replace the underlying object if needed.

Usage typically involves requiring the delegate library and wrapping an object. For example, you can wrap an array, modify behavior by adding new methods on the wrapper, and still delegate other operations to the array. The wrapped object remains the same underlying object, so changes through the wrapper affect the original object.

Example subclassing:

class MyWrapper < SimpleDelegator

def summary

"Wrapper for: #{__getobj__.inspect}"

end

end

wrap = MyWrapper.new([1, 2, 3])

wrap.summary # => "Wrapper for: [1, 2, 3]"

wrap.length # => 3 (delegates to the wrapped array)

Relation to Delegator: SimpleDelegator provides a convenient base class for simple decorators, eliminating boilerplate while preserving the full delegation behavior. For more complex wrappers, you can still use Delegator directly or other delegation mechanisms. SimpleDelegator is a practical, minimal tool for decorating objects without changing their interfaces.