Miscellaneous

Overview

The following document discusses some proto2 features, that don't have a huge impact on message handling.

Oneofs

protobluff is capable of handling oneofs. It is even designed to handle oneofs in some edge cases, like merged messages, where multiple instances of a oneof may occur. When setting a field that is part of a oneof, protobluff ensures that the field is not overshadowed by a later instance by traversing the cursor to the end and erasing all members of the oneof.

Furthermore, for each oneof, the code generator will create a function to determine which member of a oneof is currently active. This function returns a tag number and can be used inside a switch statement.

Extensions

Extensions are implemented as a linked list of descriptors. They may be defined in file or message scope (the latter are known as nested extensions). The code generator will infix extensions with _X_, in order to avoid name clashes with existing fields. Extensions are initialized automatically upon start up of the program through constructor attributes.

Packages

If a .proto file defines a package, the name of the package is prefixed to all variables and functions defined inside that file. This is especially useful to avoid name clashes between packages.

Deprecations

Inside a .proto schema file, fields, messages, enums and enum values can be annotated with the deprecated option. protobluff will flag all functions that access the annotated structure with PB_DEPRECATED, a compiler attribute to signal deprecated access. This will trigger warnings during compilation without any runtime penalty.