dispatch-conditional-types-with-builtin-types.ts

type Action =
  | {
      type: "INIT";
    }
  | {
      type: "SYNC";
    }
  | {
      type: "LOG_IN";
      emailAddress: string;
    }
  | {
      type: "LOG_IN_SUCCESS";
      accessToken: string;
    };

// 用类型查询查出Action中所有type的联合类型
type ActionType = Action["type"];

// 把类型中key为"type"去掉
type ExcludeTypeField<A> = { [K in Exclude<keyof A, "type">]: A[K] };

type ExtractActionParameters<A, T> = A extends { type: T } ? A : never
// 把参数对象中的type去掉
// Extract<A, { type: T }会挑选出能extend { type: T }这个结构的Action中的类型
type ExtractActionParametersWithoutType<A, T> = ExcludeTypeField<ExtractActionParameters<A, T>>;

type ExtractSimpleAction<A> = A extends any
  ? {} extends ExcludeTypeField<A>
    ? A
    : never
  : never;

type SimpleActionType = ExtractSimpleAction<Action>["type"];
type ComplexActionType = Exclude<ActionType, SimpleActionType>;

// 简单参数类型
function dispatch<T extends SimpleActionType>(type: T): void;
// 复杂参数类型
function dispatch<T extends ComplexActionType>(
  type: T,
  args: ExtractActionParametersWithoutType<Action, T>
): void;
// 实现
function dispatch(arg: any, payload?: any) {}

dispatch("SYNC");

dispatch('LOG_IN', {
  emailAddress: 'ssh@qq.com'
})


export {}