Search documentation

Search by topic, API name, or import path.

GitHub ↗

variable / @typed/fx

RefArray.head

Gets the first element of a RefArray as a Filtered.

Package version
2.0.0-beta.13
Category
Optional queries
Since
1.18.0
Member of
RefArray

Import

import { RefArray } from "@typed/fx";

Access RefArray.head through the imported RefArray export. Its declaration below describes the member.

This public exposure is a re-export. Its import path is supported; declaration documentation is shared with the other public exposures below.

Signatures

export declare const head: <A, E, R>(ref: RefArray<A, E, R>) => RefSubject.Filtered<A, E, R>;

Why

Models the possibly absent result of head as Filtered state, so absence stays explicit while later source versions can make a value available.

Ownership and lifetime

The head view retains no independent value. Its Effect read fails with NoSuchElement while absent; the observing Scope owns and finalizes its Fx subscription.

Examples

import { Effect } from "effect"
import * as RefArray from "@typed/fx/RefArray"

const program = Effect.gen(function* () {
  const items = yield* RefArray.make([1, 2, 3, 4, 5])

  const head = RefArray.head(items)
  const value = yield* head
  console.log(value) // 1

  // If array becomes empty, Filtered will fail
  yield* RefArray.set(items, [])
  // yield* head would fail with NoSuchElementError
})

Other public imports

These import paths expose the same declaration. Each page retains its own public name and signature.

Source