Variable firstConst

Type Declaration

• • <const Ar extends readonly unknown[]>(
        array: Ar,
    ): Ar extends readonly []
        ? Readonly<{}>
        : Ar extends readonly [E, unknown]
            ? Readonly<{ value: E }>
            : Ar extends readonly [E, E]
                ? Readonly<{ value: E }>
                : Optional<Ar[number]>

  • Returns the first element of an array as an Optional.

    Type Parameters

    • const Ar extends readonly unknown[]

    Parameters

    • array: Ar

    Returns Ar extends readonly []
        ? Readonly<{}>
        : Ar extends readonly [E, unknown]
            ? Readonly<{ value: E }>
            : Ar extends readonly [E, E]
                ? Readonly<{ value: E }>
                : Optional<Ar[number]>

    Example

    const users = [{ id: 1 }, { id: 2 }];
    const empty: { id: number }[] = [];
    
    const first = Arr.head(users);
    const none = Arr.head(empty);
    
    assert.deepStrictEqual(first, Optional.some({ id: 1 }));
    assert.deepStrictEqual(none, Optional.none);
    Copy