如何从字符串中获取 TypeScript 类型名称？

Question

所以我有一个格式为

{ 'type': type }

的类型映射，并想在通用函数中使用它来“动态”确定返回类型，但是它不起作用。

代码如下：

// Using type instead of interface. I believe it doesn't make any difference?
type SupportedPropertyTypes = {
  string: string,
  number: number,
  boolean: boolean,
  object: any
}

type PropertyType = keyof SupportedPropertyTypes

type PropertyDefinition<T extends PropertyType, N = false> = {
  type: T,
  nullable?: N,
  fallback?: PropertyValue<T,N> | (() => PropertyValue<T,N>)
}

type StorageConfig = {
  namespace: string,
  properties: {
    [key: string]: PropertyDefinition<PropertyType>
  }
}

type PropertyValue<T extends PropertyType, N = false> = SupportedPropertyTypes[T]
  | (() => SupportedPropertyTypes[T])
  | (N extends true ? null : never)

const config = {
  namespace: 'foo',
  properties: {
    foo: { type: 'string' },
    bar: { type: 'number', fallback: 1338 },
    baz: { type: 'boolean', nullable: true },
    complicatedThing: {
      type: 'object',
      nullable: true,
      fallback: () => ({
        foo: 'bar',
        bar: 'baz',
        arr: [1,2],
      })
    }
  }
}

function getFallback<TProps extends StorageConfig['properties'], T extends keyof TProps> (key: T, props: TProps) {
  return typeof props[key].fallback == 'function'
    ? props[key].fallback()
    : props[key].fallback
}

// Expected: const foo: { foo: string, bar: string, arr: number[] }
// Got: error
const foo = getFallback('complicatedThing', config.properties)

这里出现错误：

Argument of type '{ foo: { type: string; }; bar: { type: string; fallback: number; }; baz: { type: string; nullable: boolean; }; complicatedThing: { type: string; nullable: boolean; fallback: () => { foo: string; bar: string; arr: number[]; }; }; }' is not assignable to parameter of type '{ [key: string]: PropertyDefinition<keyof SupportedPropertyTypes, false>; }'.
  Property 'foo' is incompatible with index signature.
    Type '{ type: string; }' is not assignable to type 'PropertyDefinition<keyof SupportedPropertyTypes, false>'.
      Types of property 'type' are incompatible.
        Type 'string' is not assignable to type 'keyof SupportedPropertyTypes'.(2345)

根据 here 和 here 的解决方案编写了这段代码，但我可能仍然遗漏了一些东西。