Hands-On Software Engineering with Golang

Modeling field unions

One frequent requirement for many kinds of applications is the ability to model unions. A union is a special kind of value that can have multiple representations, all of which point to the same location in memory. The use of shared memory implies that every time we write a value to a particular union field, any attempt to read one of the other union fields will result in garbled data.

The concept of unions extends quite nicely to protocol buffers. If you are working with messages that contain multiple fields where, at most, one field can be set at any given time, you can reduce the amount of required memory by grouping all these fields in a union.

A union definition begins with the oneof keyword, followed by the field ...