@pacote/option

Option type inspired by Rust. It represents an optional value, an Option is either Some concrete value or it is None.

Installation

yarn add @pacote/option

Usage

import { None, Some, map } from '@pacote/option'

function divide(numerator: number, denominator: number): Option<number> {
  return denominator === 0 : None ? Some(numerator / denominator)
}

map(n => n + 1, divide(4, 2)) // => Some(3)
map(n => n + 1, divide(4, 0)) // => None

Type

Option<T> = None | Some<T>

Constructors

None: None

None represents no value.

Some<T>(value: T): Some<T>

Some() represents a value of type T.

Functions

ofNullable<T>(value?: T | null): Option<T>

Creates a new instance of Option based on the value being passed. If null or undefined, it returns None. Otherwise, it returns Some(value).

isSome<T>(option: Option<T>): boolean

Returns true if the passed option is a Some. Otherwise, it returns false.

isNone<T>(option: Option<T>): boolean

Returns true if the passed option is a None. Otherwise, it returns false.

contains<T>(match: T, option: Option<T>): boolean

Returns true if the Some value is the same as match. Otherwise, it returns false.

flatten<T>(option: Option<Option<T>>): Option<T>

Converts Option<Option<T>> to Option<T>.

getOrElse<T>(onNone: () => T, option: Option<T>): T

Returns the value contained in the option. If the option is None, it evaluates the provided function for an alternative.

map<T, U>(fn: (value: T) => U, option: Option<T>): Option<U>

Maps an Option<T> to Option<U> by applying a function to a contained value.

flatMap<T, U>(fn: (value: T) => Option<U>, option: Option<T>): Option<U>

Returns None if the option is None, otherwise calls the function with the wrapped value and returns the result.

fold<T, U>(onSome: (value: T) => U, onNone: () => U, option: Option<T>): U

Applies the onSome function to the contained value, otherwise it computes a default using onNone.

filter<T>(predicate: (value: T) => boolean, option: Option<T>): Option<T>

Returns None if the option is None, otherwise calls predicate with the wrapped value and returns:

• Some(T) if predicate returns true, and
• None if predicate returns false.

or<T>(alternative: Option<T>, option: Option<T>): Option<T>

Returns the option if it contains a value, otherwise returns the alternative.

and<T>(alternative: Option<T>, option: Option<T>): Option<T>

Returns None if the option is None, otherwise returns the alternative.

License

MIT © Luís Rodrigues.