True Myth / maybe / get

Function: get()

Call Signature

get<T, K>(key, maybeObj): Maybe<NonNullable<T[K]>>

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

Type Parameters

T

T extends object

K

K extends string | number | symbol

Parameters

key

K

The key to pull out of the object.

maybeObj

Maybe<T>

The object to look up the key from.

Returns

Maybe<NonNullable<T[K]>>

Call Signature

get<T, K>(key): (maybeObj) => Maybe<NonNullable<T[K]>>

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

Type Parameters

T

T extends object

K

K extends string | number | symbol

Parameters

key

K

The key to pull out of the object.

Returns

(maybeObj): Maybe<NonNullable<T[K]>>

Parameters

maybeObj

Maybe<T>

Returns

Maybe<NonNullable<T[K]>>