Why cannot C# generics derive from one of the generic type parameters like they can in C++ templates? [duplicate]

by

Well, start by asking yourself what could possibly go wrong with class C<T> : T { }. A huge number of things come immediately to mind:

What if T is a struct? What if T is a sealed class type? What if T is an interface type? What if T is C<T>?! What if T is a class derived from C<T>? What if T is an abstract type with an abstract method? What if T has less accessibility than C ? What if T is System.ValueType? (Can you have a non-struct which inherits from System.ValueType?) What about System.Delegate, System.Enum, and so on?

Those are the easy, obvious ones. The proposed feature opens up literally hundreds, if not thousands of more subtle questions about the interaction between the type and its base type, all of which would have to be carefully specified, implemented and tested. We’d undoubtedly miss some, and thereby cause breaking changes in the future, or saddle the runtime with implementation-defined behaviour.

The costs would be enormous, so the benefit had better be enormous. I’m not seeing an enormous benefit here.

More Related Contents:

  1. Static Generic Class as Dictionary
  2. explicitly cast generic type parameters to any interface
  3. How do I use reflection to call a generic method?
  4. Passing arguments to C# generic new() of templated type
  5. What exactly is an “open generic type” in .NET? [duplicate]
  6. Generics in C#, using type of a variable as parameter [duplicate]
  7. Create instance of generic type whose constructor requires a parameter?
  8. A generic list of anonymous class
  9. Why must I provide explicitly generic parameter types While the compiler should infer the type?
  10. Func with out parameter
  11. How to call .NET methods from Excel VBA?
  12. How to compare values of generic types?
  13. What does “T” mean in C#?
  14. Convert string to nullable type (int, double, etc…)
  15. Resolve assembly references from another folder
  16. Convert DataTable to generic List?
  17. Try-catch speeding up my code?
  18. Should we always include a default constructor in the class?
  19. What does denote in C# [duplicate]
  20. Why does C#/CLR not support method override co/contra-variance?
  21. .NET 4.0 and the dreaded OnUserPreferenceChanged Hang
  22. Can I have a variable number of generic parameters?
  23. Returning ‘IList’ vs ‘ICollection’ vs ‘Collection’
  24. Are static indexers not supported in C#? [duplicate]
  25. Which C# method overload is chosen?
  26. The component does not have a resource identified by the uri
  27. Can you have multiple enum values for the same integer? [duplicate]
  28. Retrieve JIT output
  29. Where is the .NET JIT-compiled code cached?
  30. C# generic methods, type parameters in new() constructor constraint

Leave a Comment