ReactiveDag.KeyRule behaviour (reactive_dag v0.16.0)

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How a change to a child propagates to a parent — the op-aware propagation seam. When changed keys of child feed parent, the rule decides which of the parent's keys become dirty:

  • {:keys, mapped} — a bounded, per-key fan-out (identity or a remap).
  • :all — the change fans out to the WHOLE parent cell (recompute all its keys). Needed when a single input change can affect arbitrary output keys (a fold's aggregate, a vanished key a relation must re-judge).

This one callback generalizes both hosts' propagation:

  • cascade — a uniform key_rule: :identity | :all field per cell: :identity → {:keys, changed}, :all → :all.

  • compliance portal — a per-op, per-WHICH-input rule: e.g. product and relation return :all when their fn leg changed but pass keys through when their members leg changed. rule/3 sees parent, the specific child (which input), and changed, so it can express exactly that.

This module is ALSO the default implementation — the identity rule — so the reference module satisfies its own behaviour; a host provides its own module only for a richer algebra.

Summary

Types

key()
result()

Callbacks

rule(parent, child, changed)

Given a parent cell, the specific child input id whose keys changed, and the changed keys, return how they propagate to the parent.

Functions

identity(parent, child, changed)

The trivial identity rule — pass the changed keys straight through.

Types

key()

@type key() :: String.t()

result()

@type result() :: :all | {:keys, [key()]}

Callbacks

rule(parent, child, changed)

@callback rule(
  parent :: ReactiveDag.Cell.t(),
  child :: ReactiveDag.Cell.id(),
  changed :: [key()]
) ::
  result()

Given a parent cell, the specific child input id whose keys changed, and the changed keys, return how they propagate to the parent.

Functions

identity(parent, child, changed)

@spec identity(ReactiveDag.Cell.t(), ReactiveDag.Cell.id(), [key()]) :: result()

The trivial identity rule — pass the changed keys straight through.