What are the differences between `ToXXXX` and `AsXXXX` conversion methods?

Is there any semantic difference between ToXXXX conversion methods and AsXXXX开发者_Go百科 conversion methods in the .NET framework?

Examples of such methods are Object.ToString and Enumerable.AsEnumerable<T>.

If method returns the same instance but casted to another type, use AsXXX method. If method consntructs new instance of unrelated type using object data, use ToXXX method.