types

types.ts

export type None = null | undefined;

export type Nullable<T> = T | None;

/** Make all of T's properties nullable*/
export type NullableOfType<T> = {
  [P in keyof T]: Nullable<T[P]>;
};

/** Correct type for Object.entries(myobj) */
export type Entries<T> = {
  [K in keyof T]: [K, T[K]];
}[keyof T][];

/** ValueOf<{something: true, other: 1}> -> true | 1 */
export type ValueOf<T> = T[keyof T];

/** Matches any [primitive value](https://developer.mozilla.org/en-US/docs/Glossary/Primitive).  */
export type Primitive =
  | null
  | undefined
  | string
  | number
  | boolean
  | symbol
  | bigint;

function isNone<T>(value: Nullable<T>): value is None {
  return value === null || value === undefined;
}

function isSome<T>(value: Nullable<T>): value is T {
  return !isNone(value);
}

/** helper type-level function to expand a given type to show all of its inferred fields when hovered.
 * (this is a workaround for the fact that VSCode doesn't show inferred fields when hovering, only the Supertype(s) of the union)
 *
 * Say you have a few simple types:
 * ```ts
 * type Hat = { hatBrand: string };
 * type Shirt = { shirtSize: number };
 * type Outfit = { isFavorite: boolean; isFormal: boolean; } & Hat & Shirt;
 * ```
 * when you hover over `Outfit` in your editor, you'll see:
 * ```ts
 * type Outfit = { isFavorite: boolean; isFormal: boolean; } & Hat & Shirt;
 * ```
 *
 * when what you actually want (and this helper gives you) is
 * ```ts
 * type Outfit = {
 *   isFavorite: boolean;
 *   isFormal: boolean;
 *   hatBrand: string;
 *   shirtSize: number;
 * }
 * ```
 * https://github.com/microsoft/vscode/issues/94679 */
export type Expand<T> = T extends infer O ? { [K in keyof O]: O[K] } : never;