Errors in UDL

You expose our error example in UDL like:

[Error]
enum ArithmeticError {
  "IntegerOverflow",
};


namespace arithmetic {
  [Throws=ArithmeticError]
  u64 add(u64 a, u64 b);
}

Note that in the above example, ArithmeticError is "flat" - the associated data is not exposed - the foreign bindings see this as a simple enum-like object with no data. If you want to expose the associated data as fields on the exception, use this syntax:

[Error]
interface ArithmeticError {
  IntegerOverflow(u64 a, u64 b);
};

Interfaces as errors

In our error interface example we are throwing the object MyError.

namespace error {
  [Throws=MyError]
  void bail(string message);
}

[Traits=(Debug)]
interface MyError {
  string message();
};