Fixed-dependency bindings

bindSignal source target write and bindMemo source target write copy one source into a target. The source is fixed when the binding is created. Use this for a view property or another external target whose value comes from one signal or memo.

open Ranvier

type Label () =
    member val Text = "" with get, set

use graph = new Graph ()
use active = graph.Activate ()
let name = createSignal "Ada"
let label = Label ()
bindSignal name label (fun target value -> target.Text <- value)
flush ()
printfn "%s" label.Text // Ada
name.Value <- "Grace"
printfn "%s" label.Text // Grace

The first write runs in the next flush. Outside a batch or an existing flush, the graph requests that flush as part of creating the binding. A binding created in a batch waits for its flush, and several source writes before that flush produce one write of the current value.

Choose a binding, memo or effect

• Bind a signal when its value can be copied directly to the target.
• Derive a value with a memo, then use bindMemo when the target needs that value.
• Use an effect for work whose dependencies depend on tracked reads in its body.

Reads inside write are untracked: reading a second signal there does not make it a dependency. write must not create reactive nodes or register cleanup. Create those resources in the enclosing scope, and use cleanup for their lifetime.

Equality, pending values and failures

A source's equality cutoff applies before the binding writes. An equal signal write does nothing; a memo that recomputes to an equal value leaves the target unchanged. Configure equality on the source, using the graph policy or a per-node comparer.

While a memo is pending or failed, its target keeps its last value. A memo that has never settled does not write an initial value until it becomes ready. A throwing writer does not stop other queued work; the next source change can run the writer again.

Lifetime

Both factories return unit. The binding belongs to the owner current at creation, and disposal of that owner releases the source dependency. A binding created in an effect's run is disposed before the next run. Use a root when several bindings should be stopped together.

For measurements against equivalent effects, see the method and limitations in the binding benchmarks.