Lyric

What changed in v2.10.0 — 2026-08-22

An attribute argument may name an enum variant. The bytecode format goes 3.3 → 3.4, and this is the first change to it that an older reader cannot ignore — see below.

Added

• A unit enum variant is an attribute argument.

  pub enum Layout { Packed, Separate }
  
  pub struct Saved :: [OnFunction] { layout: Layout = Layout.Packed }
  
  @Saved { layout = Layout.Separate }
  pub fn store(): void { }
  

  A vocabulary written as an enum is checked by the TYPE SYSTEM at the use site: Layout.Seperate is a compile error, where the same typo in a string is a row nobody ever matches — the fault class attributes closed for entry points, one field deeper. It works as a written argument, as a field default, and through a let bound to a variant, because one resolution walk answers all three.

  A variant with a payload is refused, and the message says why rather than repeating "must be a literal": a row holds one value per field, and a payload is values of its own.

  A host reads both halves — Text is the qualified variant (Layout.Separate), AsInt its tag. The disassembler prints the name too.

Changed

• Bytecode format 3.4: ConstValue gains one form, an attribute value of enum type written as the variant's tag. The value names no enum — the field's type does, and the enum's entry names its variants, so the name is resolved rather than stored twice.

  The compatibility note that matters: the Attributes section is skippable as a whole, but a reader that does read it meets a tag it has no case for. A module whose attribute rows use an enum value therefore does not load on a runtime older than this one; a 3.4 module without such a value loads unchanged. That is the same forward path co.next() took in 2.2.0 — the module that uses the new thing is the module that needs the new runtime.

• LYR-SEM0066 says what it now allows: a number, a string, a char, a bool, a unit enum variant, or a let bound to one.

The full changelog →