SwitchRef

On/off toggle. Semantic alternative to CheckboxRef: same wire shape, different affordance (shadcn Switch).

defaults (class-level)

field	type	default	notes
`label`	`str`	`""`	text next to the switch; empty means no label.
`default`	`bool`	`False`	initial on/off state seeded on mount.

Class attributes on the python SwitchRef. The python class uses default (not checked) to keep the wording neutral; on the wire / slice the canonical state field is checked. mount_props emits {"label": cls.label, "checked": cls.default} so the slice factory is identical to CheckboxRef.

interactions

op	dir	payload	nu method	notes
`write`	server -> tab	`bool`	`store`	canonical push or reset; replaces the local checked state.
`read`	server -> tab	request `null`; resp `bool`	(via `aeval`)	request/response, correlated by `id`; resolves the live value.
`notify`	tab -> server	`null`	`changed`	emitted on every user toggle of the switch.

SwitchRef.aeval ships a read via session.aread and returns the bool. SwitchRef.store(value) compiles to write. SwitchRef.changed() is the standard Changed subscription.

wire payloads

// mount field entry (inside the mount payload)
{"path": "HomePage.notify", "type": "SwitchRef", "props": {"label": "Notifications", "checked": false}}

// server pushes a value
{"op": "write",  "ref": "HomePage.notify", "payload": true}

// server fetches
{"op": "read",   "ref": "HomePage.notify", "payload": null, "id": "ab12"}
{"op": "read",   "ref": "HomePage.notify", "payload": true, "id": "ab12"}

// browser tells server the user toggled
{"op": "notify", "ref": "HomePage.notify", "payload": null}

write and read-response payloads are msgpack bools. notify and read-request payloads are msgpack nil.

renderer

web/src/refs/switch.tsx. shadcn Switch (from @/components/ui/switch, wrapping radix-ui's Switch.Root + Switch.Thumb) wrapped in a <label> so the label text is also a click target.

slice shape

{
  type: "SwitchRef",
  value: null,
  label: string,
  checked: boolean,
  write: (v: unknown) => void,
  get: () => boolean,
}

Seeded from field.props on mount. write coerces non-bool / nil payloads via Boolean(v). get reads the live slice to avoid stale closures.

edge cases

write payload is msgpack nil (Nu sentinel): coerced to false.
write payload is non-bool: Boolean(v) coercion; no error frame.
slot never written and no props on mount: slice defaults to checked=false, label="".
empty label: the trailing <span> is omitted; only the switch is clickable.
no debounce: each user toggle emits one notify.

non-goals

no tri-state / indeterminate variant.
no size / color variants on the python side; renderer uses shadcn defaults.
no icon slots inside the switch thumb.
no disabled prop on the Ref; disabled state belongs to a future form-level concern.