typia/src/Resolved.ts

Superfast runtime validators with only one line

import { Equal } from "./typings/Equal";
import { IsTuple } from "./typings/IsTuple";
import { NativeClass } from "./typings/NativeClass";
import { ValueOf } from "./typings/ValueOf";

/**
 * Resolved type erased every methods.
 *
 * `Resolved` is a type of TMP (Type Meta Programming) type which converts
 * its argument as a resolved type that erased every method properties.
 *
 * If the target argument is a built-in class which returns its origin primitive type
 * through the `valueOf()` method like the `String` or `Number`, its return type would
 * be the `string` or `number`. Otherwise, the built-in class does not have the
 * `valueOf()` method, the return type would be same with the target argument.
 *
 * Otherwise, the target argument is a type of custom class, all of its custom methods
 * would be erased and its prototype would be changed to the primitive `object`.
 * Therefore, return type of the TMP type finally be the resolved object.
 *
 * Before                  | After
 * ------------------------|----------------------------------------
 * `Boolean`               | `boolean`
 * `Number`                | `number`
 * `BigInt`                | `bigint`
 * `String`                | `string`
 * `Class`                 | `interface`
 * Native Class or Others  | No change
 *
 * @template T Target argument type.
 * @author Jeongho Nam - https://github.com/samchon
 * @author Kyungsu Kang - https://github.com/kakasoo
 */
export type Resolved<T> =
  Equal<T, ResolvedMain<T>> extends true ? T : ResolvedMain<T>;

type ResolvedMain<T> = T extends [never]
  ? never // (special trick for jsonable | null) type
  : ValueOf<T> extends boolean | number | bigint | string
    ? ValueOf<T>
    : T extends Function
      ? never
      : T extends object
        ? ResolvedObject<T>
        : ValueOf<T>;

type ResolvedObject<T extends object> =
  T extends Array<infer U>
    ? IsTuple<T> extends true
      ? ResolvedTuple<T>
      : ResolvedMain<U>[]
    : T extends Set<infer U>
      ? Set<ResolvedMain<U>>
      : T extends Map<infer K, infer V>
        ? Map<ResolvedMain<K>, ResolvedMain<V>>
        : T extends WeakSet<any> | WeakMap<any, any>
          ? never
          : T extends NativeClass
            ? T
            : {
                [P in keyof T]: ResolvedMain<T[P]>;
              };

type ResolvedTuple<T extends readonly any[]> = T extends []
  ? []
  : T extends [infer F]
    ? [ResolvedMain<F>]
    : T extends [infer F, ...infer Rest extends readonly any[]]
      ? [ResolvedMain<F>, ...ResolvedTuple<Rest>]
      : T extends [(infer F)?]
        ? [ResolvedMain<F>?]
        : T extends [(infer F)?, ...infer Rest extends readonly any[]]
          ? [ResolvedMain<F>?, ...ResolvedTuple<Rest>]
          : [];