C# Example

// Bridge Design Pattern
//
// Intent: Lets you split a large class or a set of closely related classes into
// two separate hierarchies—abstraction and implementation—which can be
// developed independently of each other.
//
//               A
//            /     \                        A         N
//          Aa      Ab        ===>        /     \     / \
//         / \     /  \                 Aa(N) Ab(N)  1   2
//       Aa1 Aa2  Ab1 Ab2

using System;

namespace RefactoringGuru.DesignPatterns.Bridge.Conceptual
{
    // The Abstraction defines the interface for the "control" part of the two
    // class hierarchies. It maintains a reference to an object of the
    // Implementation hierarchy and delegates all of the real work to this
    // object.
    class Abstraction
    {
        protected IImplementation _implementation;

        public Abstraction(IImplementation implementation)
        {
            this._implementation = implementation;
        }

        public virtual string Operation()
        {
            return "Abstract: Base operation with:\n" +
                _implementation.OperationImplementation();
        }
    }

    // You can extend the Abstraction without changing the Implementation
    // classes.
    class ExtendedAbstraction : Abstraction
    {
        public ExtendedAbstraction(IImplementation implementation) : base(implementation)
        {
        }

        public override string Operation()
        {
            return "ExtendedAbstraction: Extended operation with:\n" +
                base._implementation.OperationImplementation();
        }
    }

    // The Implementation defines the interface for all implementation classes.
    // It doesn't have to match the Abstraction's interface. In fact, the two
    // interfaces can be entirely different. Typically the Implementation
    // interface provides only primitive operations, while the Abstraction
    // defines higher- level operations based on those primitives.
    public interface IImplementation
    {
        string OperationImplementation();
    }

    // Each Concrete Implementation corresponds to a specific platform and
    // implements the Implementation interface using that platform's API.
    class ConcreteImplementationA : IImplementation
    {
        public string OperationImplementation()
        {
            return "ConcreteImplementationA: The result in platform A.\n";
        }
    }

    class ConcreteImplementationB : IImplementation
    {
        public string OperationImplementation()
        {
            return "ConcreteImplementationA: The result in platform B.\n";
        }
    }

    class Client
    {
        // Except for the initialization phase, where an Abstraction object gets
        // linked with a specific Implementation object, the client code should
        // only depend on the Abstraction class. This way the client code can
        // support any abstraction-implementation combination.
        public void ClientCode(Abstraction abstraction)
        {
            Console.Write(abstraction.Operation());
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Client client = new Client();

            Abstraction abstraction;
            // The client code should be able to work with any pre-configured
            // abstraction-implementation combination.
            abstraction = new Abstraction(new ConcreteImplementationA());
            client.ClientCode(abstraction);

            Console.WriteLine();

            abstraction = new ExtendedAbstraction(new ConcreteImplementationB());
            client.ClientCode(abstraction);
        }
    }
}

Abstract: Base operation with:
ConcreteImplementationA: The result in platform A.

ExtendedAbstraction: Extended operation with:
ConcreteImplementationA: The result in platform B.