Safest Object Getter Higher-Order Function and Clousor

type-safe-getter-hoc.ts

function typeSafeGetter<V extends object>(o: V) {
	return function <
		K extends keyof V,
		P extends undefined | K = undefined,
		R = P extends K ? V[P] : V,
	>(property?: P): R {
		if (typeof o === 'undefined') throw 'error';

		if (typeof property === 'undefined') {
			return o as never
		} else return o[property] as never
	}
}

type O = {
	display: 'flex' | 'block',
	dir: 'rtl' | 'ltr',
};
declare const o: O;
const get = typeSafeGetter(o);

get('dir') === 'ltr';
get().dir === 'ltr';