Question

我可以将类型作为泛型参数进行传递，但是当我使用包含类型化参数的对象时，Flow不会理解并且不会建议类型。相反，我得到一个错误。

export type TAction<T, R> = { +type: string, payload?: T, meta?: R };

function thisWorks(action: TAction<string, boolean>) {
  const {
    payload,
    meta,
  } = action;
  // Flow knows payload is string and meta a boolean
}

function doesntWork(action: TAction<{ prop1: string, prop2: string }, boolean>) {
      const {
        payload: { prop1, prop2 },
        meta,
      } = action;
        // Flow doesn't know the type of prop1, prop2 or meta
    }

流错误为：

prop1中缺少属性TAction [1] .Flow（InferError）

Answer 1

我创建了尝试说明上述问题的流程：Try it here

从中我可以看到，问题是在TAction中，元数据和有效载荷都被注释为optional properties。这就是为什么在分解有效负载之前需要对其进行检查的原因，而不是undefined。如下代码将不会出现流错误：

export type TAction<T, R> = { +type: string, payload?: T, meta?: R };

function thisWorks(action: TAction<string, boolean>) {
  const {
    payload,
    meta,
  } = action;
  // Flow knows payload is string and meta a boolean
}

function doesntWork(action: TAction<{| prop1: string, prop2: string |}, boolean>
    ) {
      const {
        payload,
        meta,
      } = action;

      if (payload) {
        const  { prop1, prop2 } = payload;
        // Do whatever is needed
      }
    }

Try with flow

或者可以更改TAction的注释，因此payload和meta将不再是可选属性，如下所示：

export type TAction<T, R> = { +type: string, payload: T, meta: R };

function thisWorks(action: TAction<string, boolean>) {
  const {
    payload,
    meta,
  } = action;
  // Flow knows payload is string and meta a boolean
}

function doesntWork(action: TAction<{| prop1: string, prop2: string |}, boolean>
    ) {
      const {
        payload: { prop1, prop2 },
        meta,
      } = action;

        // Flow doesn't know the type of prop1, prop2 or meta
    }

Try with flow

在流中传递通用参数对象

1 个答案: