A generic body cannot construct or consume a row remainder

GAP-TYPES-006

A where equation can type the remainder of a row, but no form lets a body take an abstract row apart or build one, so typestate over a row cannot be implemented generically.

Lifecycle

resolved

Owner

language

Scope

reference/spec/types.md#open-rows

Origin

metel-core#1397 documentation work on records and rows; filed as metel-core#1399

Affects · linked records

spec.types.generics.open-rows.legality-2language spec rule

spec.expressions.record-rest-patterns.legality-1language spec rule

spec.types.generics.open-rows.legality-4language spec rule

RFC-0178rfc

gapKnown gaps ↗

Gap

Resolved. RFC-0178 specifies ..name as an owned remainder binding in a record pattern, and ..expr as an owned row spread in a record literal. The type rules remove named labels from the strongest entailed decomposition, distinguish missing presence from an undetermined remainder, and define the empty remainder as {}. Bare .. remains discard-only; multiple spreads are outside the feature.

The implemented forms support that transition by matching the owned record with { token, ..rest } and spreading rest into the result record.

The syntax and behavior are specified in reference/spec/expressions.md#record-rest-patterns and reference/spec/types.md#spec.types.generics.open-rows.legality-4.

Impact

No remaining spec gap. The compiler implementation and integration fixtures are tracked by metel-core#1399.

Affects

• spec.types.generics.open-rows.legality-2
• spec.expressions.record-rest-patterns.legality-1
• spec.types.generics.open-rows.legality-4
• RFC-0178

Resolution

Resolved by RFC-0178's specification and implementation in reference/spec/expressions.md#record-rest-patterns, reference/spec/types.md#open-rows, and metel-core#1399.