A message definition uses the extends clause to specify the base message. For example:
message Foo {
string name;
}
message Bar extends Foo {
string email;
}
The resulting message type Bar contains all of the fields of its base type(s) in addition to its own,
and can be used wherever a message of type Foo is expected. A message may not override or redefine a field
that is already defined in its base class. A field defined with the same name and type will generate a warning
and be ignored. A field with the same name and a different type will result in an error.
Multiple inheritance is not currently supported and will generate an error, but may be added in a future release if there is clear demand for it. For example:
message Foo {
string name;
string email;
}
message Bar {
string name;
string telephone;
}
message Combined extends Foo, Bar {
string id;
}
The message type Combined contains four fields name, email, telephone, and id.
The fudge encoding specification allows arbitrary ordering of these within a message.
The message type Combined can be used wherever a Foo or Bar is expected. Fields with the same name
(and ordinal if specified) and same type in the base message types are accepted as in the example above.
Fields with the same name but different ordinals, or different types will result in an error.