The default replicates the behavior that existed before required and optional were added. These fields are always set when serializing, regardless of the value of __isset. This means that programmers do not have to manually maintain __isset. (Actually, the fields are not serialized if they are null in languages that allow it.) However, when deserializing, no error is thrown if a default field is not present (for example, if it was sent by an older client or server, or if it was null).
--David Bryan Duxbury wrote: > Can someone help me understand the difference between required, > default, and optional field modifiers? Required seems to make sense. > Optional seems to make sense. However, the fact that there's a third > state is quite ambiguous. > > It seems like the field modifiers should be binary - required or > optional. Leaving the modifier off should just be a shorthand for > optional. > > -Bryan
