type_utils.ts

/** Returns the codomain for a map-like type. */
export type $Values<S> = S[keyof S];

/** Omits properties over a union type, only if the union member has that property. */
export type DistributiveOmit<T, K extends keyof any> = T extends any ? Omit<T, K> : never;

/** Makes every property and array read-only, at every depth. Distributes over union types. */
export type DeepReadonly<T> =
  T extends ReadonlyArray<infer E>
    ? ReadonlyArray<DeepReadonly<E>>
    : T extends object
      ? {readonly [K in keyof T]: DeepReadonly<T[K]>}
      : T;

export type Assert<T extends true> = T;

/**
 * Ensures that all possible types of T extend BaseType.
 */
export type EnsureExtends<BaseType, T extends BaseType> = T;