hearth-hkt-derivation

Polymorphic type class derivation for higher-kinded types like F[_] is handled by Hearth macros, which generate instances for abstractions such as Functor and Foldable. It uses an erased representation to maximize compilation speed and runtime performance.

Yes, cross-version Scala derivation targets both Scala 2.13 and Scala 3. The macro-based approach requires explicit support for bridging constructors and runtime helpers to handle higher-kinded types across varied field shapes consistently.

An erased representation avoids runtime reflection and maintains binary compatibility during macro-based type class derivation. It uses a two-probe field classification to distinguish direct, invariant, and nested fields for efficient instance assembly.

The ConsK carry-and-absorb algorithm composes fields for higher-kinded type constructors during derivation. It works alongside bridge methods for type constructor summoning to handle nested F[_] fields and runtime helpers for erased HKT calls.

Derivation requires explicit support for bridging constructors, field classification, and runtime helpers to handle higher-kinded types. Without these explicit bridging mechanisms for varied field shapes, the macro cannot assemble valid type class instances.