OPTIONAL.md

Optional

Optional data structure is based on Rust Option enum. It removes the hassle of checking for null or undefined in your code and provides set of useful methods for dealing with potentially missing data.

Exports and examples

import {
  None,
  Some,
  Optional,
} from '@bausano/data-structures'

const none: Optional<number> = new None

const some: Optional<number> = none.or(new Some(3))

API

• isSome () : boolean Determines whether the option wraps any value (is instance of Some).

• isNone () : boolean Determines whether the option has no value (is instance of None).

• unwrap () : T Returns the value or throws an exception if the option is None.

• unwrapOr (def: T) : T If the option is Some, returns the value, otherwise return the def.

• unwrapOrElse (closure: () => T) : T If the option is Some, returns the value, otherwise computes the closure and returns the result.

• expect (e: Error) : T If the option is Some, return it. Otherwise, throws the error e.

• filter (predicate: (t: T) => boolean) : Optional<T> Returns None if the option is None, otherwise calls predicate with the value and returns Some if the predicate returns true, or None if the predicate returns false.

• map<U, V> (u: Optional<U>, predicate: (t: T, u: U) => Optional<V>) : Optional<V> Maps this optional to the other one. If either option is None, returns None as well. Otherwise, returns the result of the predicate.

• mapOr<U> (predicate: (t: T) => U, def: U) : U Maps T to the type U or defaults if option is None.

• mapOrElse<U> (predicate: (t: T) => U, closure: () => U) : U Maps T to the type U or defaults if option is None.

• match (some: (t: T) => void, none: () => void) : void If option is None, matches second callback, otherwise passes option value to the first callback.

• matchSome (closure: (t: T) => void) : void Runs the closure if optional is Some.

• matchNone (closure: () => void) : void Runs the closure if optional is None.

• andThen<U> (closure: (t: T) => Optional<U>) : Optional<U> Mutates the Optional's wrapped value into a new type.

• or (def: Optional<T>) : Optional<T> If this optional is None, returns def, otherwise returns this.

• orElse (closure: () => Optional<T>) : Optional<T> If this optional is None, returns def, otherwise returns this.

Notes

When using optionals as class properties, in order to change the value of the optional, you have to instantiate a new object, meaning any reference to the previous optional will still point to the old value.