Proxy

Context: Provide a surrogate or placeholder for another object to control access to it.

public interface ISubject
{
    void Request();
}

public class RealSubject : ISubject
{
    public void Request() => Console.WriteLine("RealSubject request");
}

public class Proxy : ISubject
{
    private RealSubject _realSubject;
    public void Request()
    {
        if (_realSubject == null)
            _realSubject = new RealSubject();
        // Add access control, logging, etc.
        _realSubject.Request();
    }
}

Real-world usage example

Lazy loading: A proxy delays creation of an expensive object (e.g., large image, database connection) until it’s actually needed.

Example: Entity Framework Core uses lazy loading proxies for navigation properties. Also, RealProxy for remoting (legacy) and dynamic proxies in Castle DynamicProxy.

Related sections

• 5.2 Structural patterns
• 5.2.1 Adapter
• 5.2.3 Decorator