Static factory methods vs Instance (normal) constructors?

Question

In a language where both are available, would you prefer to see an instance constructor or a static method that returns an instance?

For example, if you\'re creating

Answer 1

I write a constructor when creating the instance has no side effects, i.e. when the only thing the constructor is doing is initializing properties. I write a static method (and make the constructor private) if creating the instance does something that you wouldn't ordinarily expect a constructor to do.

For example:

public class Foo
{
   private Foo() { }

   private static List FooList = new List();
   public static Foo CreateFoo()
   {
      Foo f = new Foo();
      FooList.Add(f);
      return f;
   }
}

Because I adhere to this convention, if I see

Foo f = Foo.CreateFoo();
Bar b = new Bar();

while reading my code, I have a very different set of expectations about what each of those two lines is doing. That code isn't telling me what it is that makes creating a Foo different from creating a Bar, but it's telling me that I need to look.