TypeScript类型安全服务注册表

Question

如何在Typescript中创建类型安全服务注册表。基本上，这是一个根据参数返回具体类型的函数。

get("a") would return an object of type ServiceA.
get("b") would return an object of type ServiceB.

我按照这里的答案：https://stackoverflow.com/a/47098963/12116498，但仍然收到输入错误。

我已经将我的问题简化为以下内容，并添加了我得到的类型错误：

console.log("Test get");
console.log("Get foo from AlertsService:", get('AlertsService').foo);
console.log("Get foo from AlertsService:", get('ModalService').foo);
console.log("Get foo from AlertsService:", get('ModalService').bar);
 
function get<T extends keyof ServiceMapping>(serviceType: T): ServiceMapping[T] {
  const t: keyof ServiceMapping = serviceType;
 
  switch (t) {
    case 'AlertsService':
 
// TS2322: Type '{ type: "AlertsService"; foo: string; }' is not assignable to type 'ServiceMapping[T]'.
// Type '{ type: "AlertsService"; foo: string; }' is not assignable to type 'never'.
// The intersection 'AlertsService & ModalService' was reduced to 'never' because property 'type' has conflicting types in some constituents.
 
      return {
        type: 'AlertsService',
        foo: 'testing'
      };
    case 'ModalService':
     
// TS2322: Type '{ type: "ModalService"; foo: string; bar: string; }' is not assignable to type 'ServiceMapping[T]'.
// Type '{ type: "ModalService"; foo: string; bar: string; }' is not assignable to type 'never'.
// The intersection 'AlertsService & ModalService' was reduced to 'never' because property 'type' has conflicting types in some constituents.
     
      return {
        type: 'ModalService',
        foo: 'testing',
        bar: 'bar test'
      };
 
    default:
      throw new Error("nope");
  }
}
 
export type ServiceMapping = {
  AlertsService: AlertsService;
  ModalService: ModalService;
}
 
export type AlertsService = {
  type: 'AlertsService',
  foo: string
}
 
export type ModalService = {
  type: 'ModalService',
  foo: string,
  bar: string
}

重要的是要将返回类型限定在较窄的范围内，而不是其他类型的联合。

Answer 1

@kruschid请告诉我为什么超载不好

  type AlertsService = {
    type: 'AlertsService',
    foo: string,
  }

  type ModalService = {
    type: 'ModalService',
    foo: string,
    bar: string
  }

  function get<T extends 'AlertsService'>(arg: 'AlertsService'): AlertsService
  function get<T extends 'ModalService'>(arg: T): ModalService
  function get<T extends 'AlertsService' | 'ModalService'>(arg: T) {

    switch (arg) {
      case 'AlertsService':
        return {
          type: 'AlertsService',
          foo: 'testing'
        };
      case 'ModalService':
        return {
          type: 'ModalService',
          foo: 'testing',
          bar: 'bar test'
        };

      default:
        throw new Error("nope");
    }
  }


  const result = get('AlertsService') // AlertsService
  const result2 = get('ModalService') // ModalService