item

Module nu.domains.shape.forms.item.

Item (leaf) shape-fabric Forms: three tiers.

Three tiers that compose into ItemRef / MutableItemRef / ReactiveItemRef:

ItemForm          exists(), missing()
MutableItemForm   + set(), erase()
ReactiveItemForm  + on_change()

Pure Form mixins, no Ref or substrate knowledge. Composed into the shape/refs/* blueprints so the user-facing API comes from these Forms.

No generic peer: the Item trunk is shape-specific (a leaf value in the document model has no pure-Python collection equivalent).

No generic type params (T, InterfaceT); Refs are unparameterised.
No value_type / interface_cls properties; substrate concern, not Form.

Name	Call	Meaning
ItemForm	`ItemForm()`	Slot-level read surface for a leaf value. Ops: `exists()`, `missing()`.
MutableItemForm	`MutableItemForm()`	Slot-level write surface. Adds `set(value)` and `erase()`.
ReactiveItemForm	`ReactiveItemForm()`	Slot-level reactive surface. Adds `on_change()`.

Name	Type	Default	Meaning
`value`	`object`

Name	Type	Default	Meaning
`value`	`object`

ReactiveItemForm

Slot-level reactive surface. Adds on_change().

ReactiveItemForm()

Path nu.domains.shape.forms.ReactiveItemForm.

Methods

`.on_change()`

Subscribe to changes on this leaf.

Builds OnPrimitiveChange.

A leaf yields a scalar, not a view, so the subscription happens on the parent view's child-change channel keyed by this leaf's address. OnPrimitiveChange carries only the leaf ref (self); at runtime it calls ref._afetch_parent and ref._aaddress to resolve the parent view and address, then returns parent.on_child_change(address): one uniform path across substrates, no per-substrate override needed.

Undocumented: example.

Inherited methods

From nu.domains.shape.forms.item.MutableItemForm:

Call	Builds	Meaning
`.set(value)`	`SetCmd`	Build a `SetCmd`.
`.erase()`	`Erase`	Build an `Erase`.
`.init(value)`	`IfDo`	Set `value` iff the leaf is currently missing.

From nu.domains.shape.forms.item.ItemForm:

Call	Builds	Meaning
`.exists()`	`Exists`	Build an `Exists` query.
`.missing()`	`Missing`	Build a `Missing` query.

From nu.lang.forms.Form:

Call	Builds	Meaning
`.is_empty()`	`Bool`	True if this Form yields the EMPTY sentinel.
`.is_invalid()`	`Bool`	True if this Form yields the INVALID sentinel.
`.is_sentinel()`	`Bool`	True if this Form yields either sentinel (EMPTY or INVALID).
`.not_empty()`	`Bool`	True if this Form does not yield EMPTY.
`.not_invalid()`	`Bool`	True if this Form does not yield INVALID.

From builtins.object:

Call	Builds	Meaning
`a < b`		Return self<value.
`a <= b`		Return self<=value.
`a == b`		Return self==value.
`a != b`		Return self!=value.
`a > b`		Return self>value.
`a >= b`		Return self>=value.

Undocumented: example.

item

ItemForm

`.exists()`

`.missing()`

MutableItemForm

`.set(value)`

`.erase()`

`.init(value)`

ReactiveItemForm

`.on_change()`

On this page