Newtypes and Configs

Newtypes

A newtype wraps an existing type with a distinct name. On the wire, it encodes identically to the underlying type.

newtype UserId = u64
newtype Temperature = f32

Newtypes provide type safety in generated code -- a UserId and a raw u64 are different types even though they have the same wire representation.

newtype CompactId = u64 @varint

The annotation applies to the wire encoding of the underlying type.

Configs are compile-time constant declarations. They do not appear on the wire but are available in generated code as constants.

config MAX_PACKET_SIZE : u32 = 1500
config VERSION : string = "1.0.0"

Configs are useful for sharing magic numbers and version strings between schema and application code without encoding them in every message.

See the language specification for the full normative reference.