Type Aliases and Constants

Type Aliases

A type alias gives an existing type a new name. It's transparent — same wire encoding, same codegen, just a different name in the schema.

type UserId = u64
type Token = bytes
type DFixed = fixed64
type Labels = array<string>
type Lookup = map<string, optional<u32>>

UserId and u64 produce identical bytes. The alias exists only in the schema source, making fields more readable.

Rules

• The target must be a concrete type, not another alias
• Alias chains are rejected: type A = u64 then type B = A won't compile
• Aliases can be imported: import { UserId } from my.types

Constants

Constants are named compile-time values. They don't exist on the wire — they're resolved during compilation and disappear.

const MaxHealth : u32 = 100
const TickRate : u32 = 64

Where You Can Use Them

• Array sizes: array<u8, MaxHealth>
• Where clause bounds: where value in 0..MaxHealth
• Other constant expressions (see below)

Cross-References

Constants can reference each other with +, -, *, /:

const TicksPerSec : u32 = 64
const TickMs : u32 = 1000 / TicksPerSec   # 15
const TwoSecTicks : u32 = TicksPerSec * 2  # 128

Division truncates toward zero (integer division). Division by zero and circular dependencies are caught at compile time — you'll get a diagnostic, not a runtime panic.

Supported Types

bool, u8–u64, i8–i64, f32, f64, fixed32, fixed64. Messages, enums, unions — none of those. Constants are values, not types.