根据另一个兄弟姐妹的类型推断兄弟属性的类型答案

【问题标题】：Infer type of sibling properties based on another siblings' type根据另一个兄弟姐妹的类型推断兄弟属性的类型
【发布时间】：2021-02-25 18:47:09
【问题描述】：

我正在尝试构建一个简单的抽象来列出对象的补丁。

type MyObject = {
  attributeA: string;
  attributeB: boolean;
  attributeC: number;
};
type MyObjectKeys = keyof MyObject;

type Difference<Key extends MyObjectKeys = MyObjectKeys> = {
  // The value of this attribute should determine
  // the type of the old and new value.
  key: Key;
  oldValue: MyObject[Key];
  newValue: MyObject[Key];
};

type Patch = {
  patches: Difference[];
};

const patch: Patch = {
  patches: [
    {
      key: 'attributeB',
      // Should be inferred as boolean.
      oldValue: '',
      // Both should have the same inferred type.
      newValue: 9,
    },
  ],
};

我希望根据给定的key 输入oldValue 和newValue。不幸的是，正如代码 cmets 中所述，它不起作用。

感谢您的任何建议！

【问题讨论】：

标签： typescript types type-inference

【解决方案1】：

类型推断不是这样工作的。你应该创建一些助手：

type MyObject = {
  attributeA: string;
  attributeB: boolean;
  attributeC: number;
};
type MyObjectKeys = keyof MyObject;

type Difference<Key extends MyObjectKeys = MyObjectKeys> = {
  // The value of this attribute should determine
  // the type of the old and new value.
  key: Key;
  oldValue: MyObject[Key];
  newValue: MyObject[Key];
};

type Patch = {
  patches: Difference[];
};

function createPatch<T extends MyObjectKeys>(key: T, oldValue: MyObject[T], newValue: MyObject[T]): Difference<T> {
    return {
        key,
        oldValue,
        newValue,
    };
}

function addPatch<T extends MyObjectKeys>(key: T, oldValue: MyObject[T], newValue: MyObject[T], patch: Patch) {
    patch.patches.push(createPatch(key, oldValue, newValue));
}

const patch: Patch = {
  patches: [createPatch('attributeB', '', 9), createPatch('attributeA', '', 'newVal')],
};

addPatch('attributeC', 0, 10, patch);

【讨论】：