Composite Family¶

When To Use It¶

Use CompositeVM<VM> when the parent owns an ordered homogeneous child list and one child may be current. Tabs, note lists, result lists, and other "collection plus selection" workflows belong here.

Use the modeled composite when children are projected from models during construction instead of being provided directly.

Composite Family Deep Dive

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Shape And Ownership¶

CompositeVM adds one core concept on top of a collection container:

Current may be one child or null

Everything else follows from that contract: guarded selection helpers, foreground updates of IsCurrent, and optional builder hooks for initial selection and current-changed callbacks.

Lifecycle And Messaging¶

The composite owns both child lifecycle and selection messaging:

construct() waits for every child before the composite reports constructed
destruct() clears Current before destructing children
Current changes publish the parent Current property and the affected children's IsCurrent
AsyncSelection(true) routes selection work through the foreground dispatcher

Cross-Language Surface¶

Concept	C#	Python	TypeScript	Swift
Type	`CompositeVM<VM>`	`CompositeVM[VM]`	`CompositeVM<VM>`	`CompositeVM<VM>`
Modeled type	`CompositeVM<M, VM>`	`CompositeVMOf[M, VM]`	`CompositeVMOf<M, VM>`	`CompositeVMOf<M, VM>`
Selection slot	`Current`	`current`	`current`	`current`
Initial selector hook	`Current(selector)`	`current(selector)`	`current(selector)`	`current(selector)`

Example¶

C#PythonTypeScriptSwift

var tabs = CompositeVM<ComponentVM<TabModel>>.Builder()
    .Name("tab-bar")
    .Services(hub, dispatcher)
    .Children(() => new[] { home, settings })
    .Build();

tabs = (
    CompositeVM[ComponentVMOf[TabModel]]
    .builder()
    .name("tab-bar")
    .services(hub, dispatcher)
    .children(lambda: [home, settings])
    .build()
)

const tabs = CompositeVM.builder<ComponentVMOf<TabModel>>()
  .name("tab-bar")
  .services(hub, dispatcher)
  .children(() => [home, settings])
  .build();

let tabs = try CompositeVM<ComponentVMOf<TabModel>>.builder()
    .name("tab-bar")
    .services(hub: hub, dispatcher: dispatcher)
    .children { [home, settings] }
    .build()

Common Pitfalls¶

Using a composite for recursive trees. HierarchicalVM carries the tree semantics directly.
Forgetting that Current must always be a contained child or null.
Assuming add-after-construct auto-constructs by default. It does not unless AutoConstructOnAdd(true) is enabled.
Updating selection predicates without wiring current-changed triggers into commands that depend on selection.