Extension Object Pattern

The Extension Object Pattern is a design pattern that allows you to add new behaviors to existing classes without modifying their structure. This pattern is particularly useful in scenarios where you need to extend the functionality of a class without altering its existing code.

• Extension Object: A separate object that holds additional behavior and state for an existing class.
• Decoupling: The pattern helps in decoupling the extended behavior from the primary class.
• Composition Over Inheritance: Encourages the use of composition rather than subclassing to achieve flexibility.

The implementation of the Extension Object Pattern typically involves the following steps:

1. Define the main class that needs to be extended.
2. Create an extension object that will hold the additional behavior.
3. Integrate the extension object with the main class, allowing the main class to use the new functionality.

Here’s a simple code example in Python:

class BaseClass:
    def __init__(self):
        self.name = "Base Class"

    def display(self):
        return f"This is {self.name}"

class ExtensionObject:
    def __init__(self, base):
        self.base = base

    def extra_behavior(self):
        return f"Extra behavior added to {self.base.name}"

# Usage
base = BaseClass()
extension = ExtensionObject(base)

print(base.display())  # Output: This is Base Class
print(extension.extra_behavior())  # Output: Extra behavior added to Base Class
            

• Keep extension objects focused on specific behaviors to avoid bloating.
• Utilize interfaces to define contracts for extension objects.
• Document the purpose of each extension object for better maintainability.