[英]Is it possible to infer generic type from inside string template literal
The following piece of code does exactly what I intend to know with one caveat, I would like to avoid having to explicit the generic it needs.下面的一段代码完全符合我的意图,但需要注意的是,我想避免必须明确说明它需要的泛型。
type EventGroup = {
actions: "run" | "save"
other: "bla"
}
export type EventType<T extends keyof EventGroup> = `${T}/${EventGroup[T]}`
const t: EventType<"actions"> = "actions/run"
I would like Typescript to infer that:我想 Typescript 推断:
`actions/run` -> valid
`actions/save` -> valid
`actions/bla` -> NOT valid
`other/bla` -> valid
Which is what this code does but with an explicit generic.这就是这段代码的作用,但带有显式泛型。
You can do that with a mapped type you then take a union of the values from:您可以使用映射类型执行此操作,然后从以下位置获取值的联合:
export type EventType = {
[Key in keyof EventGroup]: `${Key}/${EventGroup[Key]}`
}[keyof EventGroup];
Testing the validity of the type:测试类型的有效性:
const t1: EventType = "actions/run"; // valid
const t2: EventType = "actions/save"; // valid
const t3: EventType = "actions/bla"; // NOT valid
const t4: EventType = "other/bla"; // valid
There are two parts to that, first the mapped type:有两个部分,首先是映射类型:
type EventType = {
[Key in keyof EventGroup]: `${Key}/${EventGroup[Key]}`
}
which evaluates as:评估为:
type EventType = {
actions: "actions/run" | "actions/save";
other: "other/bla";
}
Then we use [keyof EventGroup]
on the end to extract just the values of actions
and other
as a union.然后我们在最后使用
[keyof EventGroup]
来提取actions
的值和other
作为联合。
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