How to "wrap" implementation in C#

Question

I have these classes in C# (.NET Framework 3.5) described below:

public class Base { public int State {get; set;} public virtual int Method1(){} public virtual string Method2(){} ... public virtual void Method10(){} } public class B: Base { // some implementation } public class Proxy: Base { private B _b; public Proxy(B b) { _b = b; } public override int Method1() { if (State == Running) return _b.Method1(); else return base.Method1(); } public override string Method2() { if (State == Running) return _b.Method2(); else return base.Method2(); } public override void Method10() { if (State == Running) _b.Method10(); else base.Method10(); } }

I want to get something this:

public Base GetStateDependentImplementation() { if (State == Running) // may be some other rule return _b; else return base; // compile error }

and my Proxy's implementation will be:

public class Proxy: Base { ... public override int Method1() { return GetStateDependentImplementation().Method1(); } public override string Method2() { return GetStateDependentImplementation().Method2(); } ... }

Of course, I can do this (aggregation of base implementation):

 public RepeaterOfBase: Base // no any overrides, just inheritance { } public class Proxy: Base { private B _b; private RepeaterOfBase _Base; public Proxy(B b, RepeaterOfBase aBase) { _b = b; _base = aBase; } } ... public Base GetStateDependentImplementation() { if (State == Running) return _b; else return _Base; } ...

But instance of Base class is very huge and I have to avoid to have other additional copy in memory.

So I

have to simplify my code
have to "wrap" implementation
have to avoid a code duplication
have to avoid aggregation of any additional instance of Base class (duplication)

Is it possible to reach these goals?

Jeff Sternal · Accepted Answer · 2010-03-22 22:11:06Z

2

One solution is to extract the expensive state into its own class and share an instance of it between your concrete implementations.

answered Mar 22, 2010 at 22:11

Jeff Sternal

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2 Comments

Jeff Sternal Over a year ago

Excellent (especially after I misunderstood your problem for so long) - good luck!

garik Over a year ago

Really I have tried many variants. I need your last vote to be completely agreed. thanks. ;)

Dan Bryant · Accepted Answer · 2010-03-19 22:32:43Z

You can have your proxy object implicitly convert to Base like this:

public class BaseProxy { private Base _base; private B _runningBase; public BaseProxy(B b) { _base = new Base(); _runningBase = b; } public static implicit operator Base(BaseProxy proxy) { return (State == Running) ? proxy._runningBase : proxy._base; } }

This will allow your client code to get a reference to the underlying object (so it's not fully insulated), but it does allow you to access the proxy and have the methods behave as you expect.

Note: this doesn't actually allow the implicit usage like I thought.

But every time I need write ((Base)proxy).Method1().. :( or should to add property to the proxy: public Base Implicit { get { return ((Base) this); } } and should to call it: proxy.Implicit.Method1();
You're right, I thought it would allow an implicit '.', but it doesn't.

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