[kentonv]

> If A has field 1 types as an int, and B has field 1 typed as a string, an A message with field 1 set will not parse as a B message.

In the C++ reference implementation, which I wrote, this is not true. The field 1 with the wrong wire type would be treated as an unknown field, not an error.

It's possible that implementations in other languages have different behavior, but that would be a bug. The C++ implementation is considered the reference implementation that all others should follow.

However, shereadsthenews' assertion is not quite right either. Specifically, a string field and a sub-message field both use the same wire type; essentially, the message is encoded into a byte string. So if message A has field 1 type string, containing some bytes that aren't a protobuf, and message B has field 1 type sub-message, then you'll get a parse error.

But it is indeed quite common that one message type parses successfully as another unrelated type.

[therein]

> In the C++ reference implementation, which I wrote, this is not true. The field 1 with the wrong wire type would be treated as an unknown field, not an error.

Yeah I was about to say, protobuf C++ implementation will definitely treat it as an unknown field. I just had it do that a few days ago. :)