factory class that prevents direct instantiation

Question

How to create a factory class that prevents direct instantiation of a class ?

say, i have class Comment that should only be instantiated from a class CommentFactory. I don't want Comment to be able to be instantiated directly.

I figured I could do this :

  public partial class Comment
  {
    private Comment(){}
    public Comment CreateComment(User user,string str)
    {
       Comment cmt=new Comment();
       user.AddComment(cmt);
       cmt.User=user;
       return cmt;       
    }
  }

is this code clean ?

now, the problem i'm facing is that the Comment is a partial class with partial implementation done by Linq to SQL. and Linq to SQL creates a public constructor of this class, so how can i circumvent this ? is there any 'trick' ?

Answer 1

If Comment and CommentFactory are in the same assembly, making all constructors of Comment internal will prevent any code outside of the assembly from creating instances of Comment.

Answer 2

You can mark the constructor internal to an assembly that CommentFactory resides in and then have consumers access the CommentFactory class. I'm not sure how else to "enforce" it.

Answer 3

What you're asking can be answered here. It's not exactly the same, but the solutions will be almost identicle.

I figure there are at least 3 tricks to solve your question, so it'll add more flexibility for you.