英文:
How to convert object of any type values, to object of string values (Typescript)?
问题
我有一个对象。/*type A = {property1: any;property2: any;}*/
我知道对象中的值都是字符串，但我不想强制类型转换。
// 我不想这样做const obj2 = obj1 as Record<keyof typeof obj1, string>
相反，我想以正确的方式推断它，使用typescript predicates。这是我的尝试。
function getIsCorrectType<T extends Record<string, any>>(obj: T): obj is Record<keyof T, string>{return true; // 假设我手动检查了每个值是否为字符串}
然而，我现在遇到了一个错误
A type predicate的type必须可分配给其parameter的type。Type 'Record<keyof T, string>' is not assignable to type 'T'.'Record<keyof T, string>' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'Record<string, any>'.Type 'string' is not assignable to type 'T[P]'.
对我来说这听起来很奇怪。我应该能够将string分配给T[P] = any，对吗？我做错了什么？是否有其他解决方案？
<details><summary>英文:</summary>I have an object.
let obj1: A;
/*
type A = {
property1: any;
property2: any;
}
*/
I know that the values in the object are all strings, but I **don't** want to forcefully typecast.
// I don't want to do this
const obj2 = obj1 as Record<keyof typeof obj1, string>
Instead, I want to infer it in the right way, using **typescript predicates**. This is my attempt to do it.
function getIsCorrectType<T extends Record<string, any>>(
obj: T
): obj is Record<keyof T, string>{
return true; // assume that I manually checked each value to be a string
}
However I now get an error
A type predicate's type must be assignable to its parameter's type.
Type 'Record<keyof T, string>' is not assignable to type 'T'.
'Record<keyof T, string>' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'Record<string, any>'.
Type 'string' is not assignable to type 'T[P]'.
To me this sounds crazy. I should be able to assign `string` to `T[P] = any`, right? What am I doing wrong? Is there any alternative solution to this?</details># 答案1**得分**: 2```typescript为了使其工作，您只需要推断一组键，而不是整个对象：const isString = (value: unknown): value is string => typeof value === 'string'const getIsCorrectType = <K extends string>(obj: Record<K, unknown>): obj is Record<K, string> =>Object.values(obj).every(isString)const x = getIsCorrectType({ 1: 'sdf' })K - 用于键的推断还添加了isString自定义类型保护
英文:
In order to make it work, you need to infer just a set of keys instead of whole object:
const isString = (value: unknown): value is string => typeof value === 'string'const getIsCorrectType = <K extends string>(obj: Record<K, unknown>): obj is Record<K, string> =>Object.values(obj).every(isString)const x = getIsCorrectType({ 1: 'sdf' })
K - is used for keys inference
Also I have added isString custom typeguard
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