User-defined conversion operator from base class

by

It’s not a design flaw. Here’s why:

Entity entity = new Body();
Body body = (Body) entity;

If you were allowed to write your own user-defined conversion here, there would be two valid conversions: an attempt to just do a normal cast (which is a reference conversion, preserving identity) and your user-defined conversion.

Which should be used? Would you really want is so that these would do different things?

// Reference conversion: preserves identity
Object entity = new Body();
Body body = (Body) entity;

// User-defined conversion: creates new instance
Entity entity = new Body();
Body body = (Body) entity;

Yuk! That way madness lies, IMO. Don’t forget that the compiler decides this at compile-time, based only on the compile-time types of the expressions involved.

Personally I’d go with solution C – and possibly even make it a virtual method. That way Body could override it to just return this, if you want it to be identity preserving where possible but creating a new object where necessary.

More Related Contents:

  1. Get int value from enum in C#
  2. Casting vs using the ‘as’ keyword in the CLR
  3. Direct casting vs ‘as’ operator?
  4. String was not recognized as a valid DateTime ” format dd/MM/yyyy”
  5. Shorter syntax for casting from a List to a List?
  6. C# “as” cast vs classic cast [duplicate]
  7. Why does “int[] is uint[] == true” in C#
  8. How do I cast int to enum in C#?
  9. How do I provide custom cast support for my class?
  10. Convert base class to derived class [duplicate]
  11. convert double to int
  12. Cast LINQ result to ObservableCollection
  13. c# Creating an unknown generic type at runtime
  14. How to cast Object to its actual type?
  15. In C#, is it possible to cast a List to List?
  16. Casting vs Converting an object toString, when object really is a string
  17. ‘casting’ with reflection
  18. Why should casting be avoided? [closed]
  19. Why can’t I cast from a List to List?
  20. C#: Dynamic runtime cast
  21. Why Enumerable.Cast raises an InvalidCastException?
  22. Cast Int to Generic Enum in C#
  23. Casting object to int throws InvalidCastException in C#
  24. C# params object[] strange behavior
  25. Why does null need an explicit type cast here? [duplicate]
  26. C# : ‘is’ keyword and checking for Not
  27. Cast IList to List
  28. Casting array to IEnumerable
  29. IsAssignableFrom, IsInstanceOfType and the is keyword, what is the difference?
  30. When to use a Cast or Convert

Leave a Comment