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Bynk

`bynk.agents.non_zeroable_state_field`

[bynk.agents.non_zeroable_state_field] agent `Gauge` store cell `level` has no
defined zero value, so a fresh key cannot be initialised

What it means

Section titled “What it means”

An agent’s store field has a type with no zero value. Bynk initialises a never-seen key’s state automatically, so every field needs a well-defined starting value. Types that have one include Int (0), Bool (false), String (""), Option[T] (None), and records of zeroable fields. Types that do not include opaque types, sum types (other than Option), and refined types that exclude their zero.

agent Gauge {
  key id: String
  store level: Cell[Int where Positive]   -- Positive excludes 0 — no zero value
}

Fix

Section titled “Fix”

  • Add an initialiser. Give the field an explicit starting value with = <value>; any type becomes admissible, including sums (a state machine’s initial state) and refined types:

    store level: Cell[Int where Positive] = 1

    The initialiser must be a compile-time value; see bynk.agents.bad_state_initialiser.

  • Use Option for “not set yet”. None is a valid zero and means “never set” (store level: Cell[Option[Int]]).

  • Relax the refinement so the zero is admitted (e.g. NonNegative instead of Positive, since 0 satisfies NonNegative).

Section titled “Related”