Language Design: Unions in Bytecode (WIP)

Overview

When designing bytecode operations for unions, encoding what is being done (instead of how) leads to desirable design properties:

1. Higher resilience against changes to the union definition, which in turn improves support for separate compilation.
2. Ability to let the runtime pick the best memory representation for a given union type, which in turn allows adjusting this choice across subsequent runtime versions without recompiling from source code.

Bytecode Operations

• new-union($union_id, $union_variant_id, $object) -> $union_value:
  Creates a union value from the given object.
• load-union-tag($union_value) -> $union_tag:
  Retrieves a union value’s tag that represents the active variant.
• load-union-object($union_value) -> $object:
  Retrieves a union value’s object. (Inverse of new-union.)
• load-component($object, $index) -> $object_component:
  (optional) Retrieves a component of an object for pattern matching.
  Shape-independent operation compared to loading field or calling a getter.

Examples