Proxy Pattern

Introduction

The Proxy Pattern is a structural design pattern that provides an object representing another object. It acts as a surrogate or placeholder, controlling access to it. Proxies are useful in various scenarios, such as lazy initialization, access control, logging, and monitoring.

Definition

The Proxy Pattern involves creating a proxy class that implements the same interface as the real subject. This enables the proxy to manage the lifecycle and access control of the subject.

Structure

The Proxy Pattern consists of the following components:

• Subject: The interface that both the RealSubject and Proxy implement.
• RealSubject: The class that defines the actual object to be represented.
• Proxy: The class that acts as a substitute for the RealSubject, controlling access to it.

Implementation

Here’s a basic implementation of the Proxy Pattern in Python:

class Subject:
    def request(self):
        pass

class RealSubject(Subject):
    def request(self):
        return "RealSubject: Handling request."

class Proxy(Subject):
    def __init__(self, real_subject):
        self._real_subject = real_subject

    def request(self):
        # Additional functionality can be added here
        return f"Proxy: Logging before request.\n{self._real_subject.request()}"

# Client code
real_subject = RealSubject()
proxy = Proxy(real_subject)
print(proxy.request())
                

Use Cases

The Proxy Pattern can be beneficial in several scenarios:

1. Lazy initialization of heavy objects.
2. Access control to sensitive resources.
3. Logging and monitoring requests.
4. Remote proxy for accessing objects in a different address space.

Best Practices

When implementing the Proxy Pattern, consider the following best practices:

• Ensure the Proxy maintains the same interface as the RealSubject.
• Keep Proxy logic minimal to avoid complexity.
• Use Proxy for cross-cutting concerns like logging and access control.

FAQ

Flowchart

graph TD;
    A[Client] -->|Requests| B[Proxy];
    B -->|Delegates| C[RealSubject];
    C -->|Returns Response| B;
    B -->|Returns Response| A;