Why is this code invalid in C#?

by

The compiler requires that either the types of second and third operands are the same, or that one is implicitly convertible to the other. In your case, the types are DBNull and string, neither of which is implicitly convertible to the other. Casting either of them to object solves that.

EDIT: Looks like it is indeed legal in Java. Quite how it works out what to do when it comes to method overloading, I’m not sure… I’ve just looked at the JLS, and it’s extremely unclear about what the type of the conditional is when there are two incompatible reference types involved. The C# way of working may be more irritating occasionally, but it’s clearer IMO.

The relevant section of the C# 3.0 spec is 7.13, the conditional operator:

The second and third operands of the
?: operator control the type of the
conditional expression. Let X and Y be
the types of the second and third
operands. Then,

  • If X and Y are the same type, then this is the type of the conditional
  • Otherwise, if an implicit conversion (§6.1) exists from X to Y,
    but not from Y to X, then Y is the
    type of the conditional expression.
  • Otherwise, if an implicit conversion (§6.1) exists from Y to X,
    but not from X to Y, then X is the
    type of the conditional expression.
  • Otherwise, no expression type can be determined, and a compile-time
    error occurs.

More Related Contents:

  1. Nullable types and the ternary operator: why is `? 10 : null` forbidden? [duplicate]
  2. Conditional operator assignment with Nullable types?
  3. Nullable type issue with ?: Conditional Operator
  4. In C# why can’t a conditional operator implicitly cast to a nullable type
  5. Type result with conditional operator in C#
  6. Why doesn’t the conditional operator correctly allow the use of “null” for assignment to nullable types? [duplicate]
  7. Conditional operator cannot cast implicitly?
  8. What is the difference between null and System.DBNull.Value?
  9. What is the difference between Nullable.HasValue or Nullable != null?
  10. Nullable type is not a nullable type?
  11. C# elegant way to check if a property’s property is null
  12. What are lifted operators?
  13. How to set enum to null
  14. Type of conditional expression cannot be determined because there is no implicit conversion between ‘int’ and
  15. Compare nullable types in Linq to Sql
  16. Ternary operator VB vs C#: why resolves Nothing to zero? [duplicate]
  17. Handle DBNull in C#
  18. Linq query with nullable sum
  19. Why GetType returns System.Int32 instead of Nullable? [duplicate]
  20. Unique ways to use the null coalescing operator [closed]
  21. nullable object must have a value
  22. Where in memory are nullable types stored?
  23. How is the boxing/unboxing behavior of Nullable possible?
  24. Ternary operator is twice as slow as an if-else block?
  25. What is the default value of the nullable type “int?” (including question mark)?
  26. DBNull if statement
  27. Boxing / Unboxing Nullable Types – Why this implementation?
  28. How to get nullable DateTime out of the database
  29. Correct way to check if a type is Nullable [duplicate]
  30. Serializing a Nullable in to XML

Leave a Comment