Thank you Isaac - this is exactly what I was looking
for. Your caveats were also helpful.
Note: I would also like to thank everyone else who
responded. I should have spec'd that the object
constructors could not be exposed anywhere within the
assembly also.
--- Isaac Hepworth <[EMAIL PROTECTED]>
wrote:
> This is a pain in C# without creating a separate
> assembly and using the
> internal modifier. Times like these I wish for a
> logical unit (and
> corresponding access modifier) similar to packages
> in java. Or the C++
> concept of friend classes.
>
> As it is, I use something similar to your example.
> As written I think
> your code has some problems with the specification
> "the objects should
> not be created outside of one static function". For
> example,
> 1) clients can create a MyItfImplementorA simply by
> calling
> MyItfImplementorA.Create(TheFactory.Instance())
> 2) clients can create a MyItfImplementorA by calling
> MyItfImplementorA.Create(null)
> 3) clients can implement their own class which
> implements
> IMyInterfaceFactory and call
> MyItfImplementorA.Create(myNewFactory)
> Also, your factory singleton isn't thread-safe ;-)
>
> The code below is a slightly tighter version of the
> same principle.
>
> public interface IMyInterface { void Run(); }
>
> public class MyClass: IMyInterface {
> private MyClass() {}
> public void Run() { /* whatever */ }
> public static MyClass Create( MyFactory
> factory ) {
> if (factory == null) throw new
> Exception("Nice try");
> return new MyClass();
> }
> }
>
> public sealed class MyFactory {
> private static MyFactory _instance = new
> MyFactory(); //
> singleton
> private MyFactory() {}
> public static IMyInterface
> CreateMyInterface() {
> // logic for which concrete class
> // to instantiate goes here ...
> return /* for example */
> MyClass.Create(_instance);
> }
> }
>
> It is now impossible for clients to create a MyClass
> without using
> MyFactory.CreateMyInterface(). And note that
> MyFactory is sealed, so
> clients can't extend it and pass in an instance of
> their descendent
> class to MyClass.Create().
>
> Cheers,
>
> Isaac
>
> > -----Original Message-----
> > From: Moderated discussion of advanced .NET
> topics.
> > [mailto:[EMAIL PROTECTED]] On
> Behalf Of Stoyan Damov
> > Sent: 01 August 2002 09:23
> > To: [EMAIL PROTECTED]
> > Subject: Re: [ADVANCED-DOTNET] Need a C# pattern
> that returns
> > an Interface
> >
> >
> > Well, I guess it could look a little bit strange
> but it works and I
> > can't come up with a better idea, and because I am
> not as
> > articulate in
> > explanations as I wish, here's the commented code:
> >
> >
> > using System;
> >
> > namespace TestPattern
> > {
> >
> > // the interface
> > public interface IMyInterface
> > {
> > void Run ();
> > }
> >
> >
> > // you'll get the idea below
> > public interface IMyInterfaceFactory
> > {
> > }
> >
> >
> > // an implementor
> > public class MyItfImplementorA : IMyInterface
> > {
> > // note, the constructor is private
> > private MyItfImplementorA () {}
> >
> > public void Run ()
> > {
> > Console.WriteLine ("Running
> MyItfImplementorA");
> > }
> >
> > // see? only the factory is allowed to
> call this method
> > public static IMyInterface Create
> > (IMyInterfaceFactory factory)
> > {
> > return (new MyItfImplementorA ());
> > }
> > }
> >
> >
> > // another one
> > public class MyItfImplementorB : IMyInterface
> > {
> > private MyItfImplementorB () {}
> >
> > public void Run ()
> > {
> > Console.WriteLine ("Running
> MyItfImplementorB");
> > }
> >
> > // see? only the factory is allowed to
> call this method
> > public static IMyInterface Create
> > (IMyInterfaceFactory factory)
> > {
> > return (new MyItfImplementorB ());
> > }
> > }
> >
> >
> > // this is the factory and it is singleton
> > public class TheFactory : IMyInterfaceFactory
> > {
> > private static TheFactory instance = null;
> > private static int x = 1; // no special
> purpose
> >
> > private TheFactory () // private ctor
> (singleton)
> > {
> > }
> >
> > public static TheFactory Instance ()
> > {
> > if (instance == null)
> > instance = new TheFactory
> ();
> > return (instance);
> > }
> >
> > // this is your static method
> > public static IMyInterface CreateInstance
> ()
> > {
> > switch (x)
> > {
> > case 1:
> > x ++; // this is
> just to imitate your
> > logic where different objects are created...
> > return
> MyItfImplementorA.Create
> > (Instance ());
> > case 2:
> > x --; // here
> too...
> > return
> MyItfImplementorB.Create
> > (Instance ());
> > default:
> > return (null);
> > }
> > }
> > }
> >
> >
> > public class Test
> > {
> > public Test ()
> > {
> > }
> >
> > public void Run ()
>
=== message truncated ===
__________________________________________________
Do You Yahoo!?
Yahoo! Health - Feel better, live better
http://health.yahoo.com
You can read messages from the Advanced DOTNET archive, unsubscribe from Advanced
DOTNET, or
subscribe to other DevelopMentor lists at http://discuss.develop.com.
