[英]Typescript : generic not inferred
I'm new to Typescript, coming from Java/Kotlin.我是 Typescript 的新手,来自 Java/Kotlin。 I have this script:
我有这个脚本:
class RequestMessage<ResponseType> {}
class NewOrderRequestMessage extends RequestMessage<OrderFilled | OrderCancelled> {}
async function sendMessage<T>(requestMessage:RequestMessage<T>): Promise<T> {
return new Promise<T>((resolve, reject) => {
// ...
})
}
(async () => {
let requestMessage = new NewOrderRequestMessage()
let result = await sendMessage(requestMessage)
})()
My problem is that result type is inferred as "unknown", while I expected it to be inferred to OrderFilled | OrderCancelled
我的问题是结果类型被推断为“未知”,而我希望它被推断为
OrderFilled | OrderCancelled
OrderFilled | OrderCancelled
, as the parameter of sendMessage is a RequestMessage<OrderFilled | OrderCancelled>
OrderFilled | OrderCancelled
,因为 sendMessage 的参数是RequestMessage<OrderFilled | OrderCancelled>
RequestMessage<OrderFilled | OrderCancelled>
Typically, in Java/Kotlin, the same logic makes result
correctly inferred:通常,在 Java/Kotlin 中,相同的逻辑可以正确推断
result
:
class Promise<T>()
open class RequestMessage<T> {}
class NewOrderRequestMessage : RequestMessage<Int>() {}
fun <T> sendMessage(requestMessage: RequestMessage<T>): Promise<T> {
return Promise()
}
val requestMessage = NewOrderRequestMessage()
val result = sendMessage(requestMessage)
In this equivalent Kotlin script, result is inferred to Promise<Int>
.在这个等效的 Kotlin 脚本中,结果被推断为
Promise<Int>
。
Why couldn't it be in Typescript?为什么不能在 Typescript 中? Due to this unknown type, Typescript doesn't give me error at compilation when sendMessage returns a Promise of another type, giving me weird situations.. I expect response type to be OrderFilled or OrderCancelled, but sendMessage can actually resolve to a promise of a completely unrelated type without having any compilation error, which produces unexpected and unhandled exception at runtime.
由于这种未知类型,当 sendMessage 返回另一种类型的 Promise 时,Typescript 在编译时不会给我错误,这给我带来了奇怪的情况。我希望响应类型为 OrderFilled 或 OrderCancelled,但 sendMessage 实际上可以解析为 ZB321DE3BDC57DEFDEF8 的 ZB321DE3BDC57DEFDEF8完全不相关的类型,没有任何编译错误,这会在运行时产生意外和未处理的异常。
TS is not strongly typed language, its type system is about shape only. TS 不是强类型语言,它的类型系统只是关于形状。 That said
NewOrderRequestMessage
is no longer a generic.也就是说
NewOrderRequestMessage
不再是通用的。
If you cast it to RequestMessage<OrderFilled | OrderCancelled>
如果您将其转换为
RequestMessage<OrderFilled | OrderCancelled>
RequestMessage<OrderFilled | OrderCancelled>
then inferring will work just fine: RequestMessage<OrderFilled | OrderCancelled>
然后推断将正常工作:
interface OrderFilled {
}
interface OrderCancelled {
}
class RequestMessage<ResponseType> {}
class NewOrderRequestMessage extends RequestMessage<OrderFilled | OrderCancelled> {}
type RequestMessageWithOrder = RequestMessage<OrderFilled | OrderCancelled>
async function sendMessage<T>(requestMessage:RequestMessage<T>): Promise<T> {
return new Promise<T>((resolve, reject) => {
// ...
})
}
(async () => {
let requestMessage: RequestMessageWithOrder = new NewOrderRequestMessage()
let result = await sendMessage(requestMessage)
})()
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