ProtoDef goes far beyond the abilities of Protocol Buffers, here are few highlights:


Here’s an example with a little bit of everything

@doc """
This is a documentation attribute. It will be included in the
generated documentation.

A native type is a type which needs to be implemented in each
target language.

You would need to provide a function for reading, writing and
calculating the size of the type.

The function is annotated as an integer so that the compiler
can use it in things like array length calculations.
@type integer("u8") def_native("u8");
@type integer("u64") def_native("u64");

@doc "Native types without type annotations are opaque to the compiler."

@doc "A native type which takes a single integer argument."
@type binary("utf8")
def_native("sized_string") {
    @doc """
    Arguments can also have documentation attached to them. This
    will show up in the documentation browser.
    argument("size", stage: "read") => integer("usize");

@doc "A composite data structure which contains 3 fields."
def("position") => container {
    field("x") => ::f64;
    field("y") => ::f64;
    field("z") => ::f64;

@doc """
A more advanced composite data structure.

Demonstrates usage of virtual fields.
def("entity_data") => container {
    field("entity_id") => ::u64;

    @doc "Uses the type defined above."
    field("position") => ::position;

    @doc """
    A virtual field will exist only in the binary form, not in the
    input/output data structure. A virtual field always needs another
    field to pull its value from when serializing. In this case it
    writes the tag of the `entity_type` union field.
    virtual_field("entity_type_tag", value: "entity_type/@tag") => ::u8;

    @doc """
    A union is the only provided way to do conditionals.

    This will match on the value of the `entity_type_tag` field in the
    parent container.
    field("entity_type") => union("entity_type", tag: "../entity_type_tag") {
        variant("player", match: "0") => container {};
        variant("zombie", match: "1") => container {};

@doc """
A composite type which reads and writes a u8 size prefixed utf8

Note that since the container is `virtual`, it will not actually
exist in the input/output data structure.
This will look like a utf8 string to the programmer.
def("u8_string") => container(virtual: "true") {
    virtual_field("size", value: "string/@size") => u8;
    field("string") => sized_string(size: "../size");

@doc "Another example of a virtual container."
def("packet") => container(virtual: "true") {
    virtual_field("tag", value: "data/@tag") => ::u8;
    field("data") => union("packet_variant", tag: "../tag") {
        variant("handshake", match: "0") => container {
            field("nonce") => ::u64;
        variant("ping", match: "1") => container {
            field("nonce") => ::u64;
            field("timestamp") => ::u64;
        variant("spawn_entity", match: "2") => ::entity_data;

@doc """
Namespaces are fully supported. They can be nested, and can
have documentation attached.
namespace("test") {

  def("test") => container {};