Safely extract a key from a Maybe
of an object, returning
Just
if the key has a value on the object and
Nothing
if it does not. (Like property
but
operating on a Maybe<T>
rather than directly on a T
.)
The check is type-safe: you won't even be able to compile if you try to look up a property that TypeScript knows doesn't exist on the object.
import { get, just, nothing } from 'true-myth/maybe';
type Person = { name?: string };
const me: Maybe<Person> = just({ name: 'Chris' });
console.log(get('name', me)); // Just('Chris')
const nobody = nothing<Person>();
console.log(get('name', nobody)); // Nothing
However, it also works correctly with dictionary types:
import { get, just } from 'true-myth/maybe';
type Dict<T> = { [key: string]: T };
const score: Maybe<Dict<number>> = just({
player1: 0,
player2: 1
});
console.log(get('player1', score)); // Just(0)
console.log(get('player2', score)); // Just(1)
console.log(get('player3', score)); // Nothing
The order of keys is so that it can be partially applied:
import { get, just } from 'true-myth/maybe';
type Person = { name?: string };
const lookupName = get('name');
const me: Person = { name: 'Chris' };
console.log(lookupName(me)); // Just('Chris')
const nobody: Person = {};
console.log(lookupName(nobody)); // Nothing
The key to pull out of the object.
Safely extract a key from a
Maybe
of an object, returningJust
if the key has a value on the object andNothing
if it does not. (Likeproperty
but operating on aMaybe<T>
rather than directly on aT
.)The check is type-safe: you won't even be able to compile if you try to look up a property that TypeScript knows doesn't exist on the object.
However, it also works correctly with dictionary types:
The order of keys is so that it can be partially applied: