DDSXTY13 — Setting of @default with @optional members

The default value of an member defined with @optional is "not set".

However it is possible to also apply the @optional annotation. In this situation should the value specified in the @default override the "not set" default?

For example if MyStruct is specified as:

@mutable
struct myStruct {
  long m1;
  @optional @default(2) long m2;
}

Would the default value of m2 be "not set" or 2?

At first glance it would seem that @default should override since if that was not the desired behavior then the user could just as well omit it. On the other hand, there seems to be a bit of ambiguity. Imagine m2 is not set by the sender, would the receiver then get "not set" or 2. If it gets 2, then how would a user ever detect the lack of m2 being set which is one of the goals of optionality.

Do not allow a @default on an @optional member

The @optional annotation is incompatible with the @default annotation. When both are set it should cause an error or at least a warning that @default is ignored.