对象类型的Flowtype数组不允许额外的属性 [英] Flowtype array of object type does not allow extra properties

问题描述

我在流程中遇到了一个奇怪的错误.我只是想拥有一个接受具有 amount 属性的对象数组的函数，但是在为对象提供更多属性时出现错误.

I am having a strange error with flow. I'm simply trying to have a function that accepts an array of objects with an amount property but I'm having errors when providing objects with more properties.

const sum = (items: Array<{amount: number}>) => {/* something */}

type Item = {
  amount: number,
  name: string
};

const list: Array<Item> = [];

sum(list);

这给了我以下错误:

10: const list: Array<Item> = [];
                      ^ property `name`. Property not found in
2: const sum = (items: Array<{amount: number}>) => {/* something */}
                             ^ object type

https://flow.org/try/#0FAYw9gdgzgLgBFArgWzgXjgCgJYwKbJQBccAggE7kCGAngDwDeVyYiEMJEKARnuQL4A+AJTpBcBgHoAVAjDI8MABbYIAczjTJ-YLpg0ADnjgBJfKgwNgcOM1btOPPgBprcCMzwlY5VWuD8ANy64NDwADbYsCQU1PRmBOIYANoAusHASMiYkbDCgUA

推荐答案

类似于此处描述的问题: https://github.com/facebook/flow/issues/1644

Similar to the issue described here: https://github.com/facebook/flow/issues/1644

这是不允许的，因为您有声明

This is not allowed, because the declaration you have,

const sum = (items: Array<{amount: number}>) => {/* something */}

将允许

const sum = (items: Array<{amount: number}>) => {
    items.push({amount: 4});
};

在给出 items 声明的情况下完全有效.传递给 sum 的数组是您 Item 类型的列表，该列表需要一个 name ，此处未设置.

which is totally valid given the declaration of items. The array passed to sum is a list of your Item type, which requires a name, which isn't set here.

如前所述， $ ReadOnlyArray 可以工作，因为它是只读的，不能再添加任何项目.或者，您可以将类型定义从 sum 完全删除，让Flow推断它们，或者将 Array< {amount:number}> 更改为 Array&*; *.，因此Flow知道它是一个数组，但是会推断内容的类型.(您在评论中留下的)另一种选择是

As you mentioned, $ReadOnlyArray works, because it is read-only and can't have more items added to it. Alternatively you could drop the type definitions from sum entirely and let Flow infer them, or change Array<{amount: number}> to Array<*> so Flow knows it is an array, but will infer the type of the content. Another alternative (that you left in the comments) is

const sum = <T : {amount: number}>(items: Array<T>) => {/* something */}

这将根据您对 sum(list)的调用将 T 设置为 Item ，但限制是它将接受任何> T 是具有数字 amount 属性的对象.

which will set T to Item based on your call to sum(list), with the restriction that it will accept any T that is an object with a numeric amount property.

这可能是最好的选择.

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