Function discriminator

packages/effect/src/internal/matcher.ts:338–367

(field: D)

/** @internal */
export const discriminator = <D extends string>(field: D) =>
<
  R,
  P extends Types.Tags<D, R> & string,
  Ret,
  Fn extends (_: Extract<R, Record<D, P>>) => Ret
>(
  ...pattern: [
    first: P,
    ...values: Array<P>,
    f: Fn
  ]
) => {
  const f = pattern[pattern.length - 1]
  const values: Array<P> = pattern.slice(0, -1) as any
  const pred = values.length === 1
    ? (_: any) => _ != null && _[field] === values[0]
    : (_: any) => _ != null && values.includes(_[field])

  return <I, F, A, Pr>(
    self: Matcher<I, F, R, A, Pr, Ret>
  ): Matcher<
    I,
    Types.AddWithout<F, Extract<R, Record<D, P>>>,
    Types.ApplyFilters<I, Types.AddWithout<F, Extract<R, Record<D, P>>>>,
    A | ReturnType<Fn>,
    Pr,
    Ret
  > => (self as any).add(makeWhen(pred, f as any)) as any
}

/** @internal */
export const discriminatorStartsWith = <D extends string>(field: D) =>