Written function types are move-only, with no copy qualifier or Erased state yet

GAP-FUNCTIONS-003

A written function type is always move-only; the copy |T| -> U qualifier and the Erased (capability unknown) state are not available.

Lifecycle

planned

Owner

language

Scope

reference/spec/functions.md#first-class-functions

Origin

metel-core#1235 records pass over the limit-phrasing lint of reference/spec/functions.md

Affects · linked records

RFC-0163rfc

gapKnown gaps ↗

Gap

RFC-0166 (v0.13.0) makes a written function type lower to a concrete move-only type and erases copyability where a value flows into such a slot. The full surface (a copy |T| -> U qualifier for an explicitly copyable callable, and a distinct "capability unknown" state) is RFC-0163, rescheduled to v0.18.1, which refines the move-only state rather than replacing it.

Impact

A closure that could be copied loses that once it passes through a slot with a written function type, and there is no way to require or preserve copyability there.

Affects

• RFC-0163

Resolution

Planned, tracked as metel-core#936 (RFC-0163).