Question

我遇到错误

Cannot invoke an expression whose type lacks a call signature ... has no compatible call signatures.

关于我的一种方法，我不知道如何解决它。我已经看到了此链接cannot-invoke-an-expression-whose-type-lacks-a-call-signature

还有2个，但仍然没有设法解决

类型声明：

type ProcessMethods = "execute" | "execSpawn"

interface IDeferedCmd {
    type: ProcessMethods,
    cmd: string,
    name: string,
    resolve: IResolveFn,
    reject: IRejectFn,
    args?: Array<string>,
    options?: object


}

在我的课堂上，我有2个看起来像这样的静态方法

static execute({cmd, name}: { cmd: string, name: string }): Promise<{
        stdout: string;
        stderr: string;
    }>

static execSpawn({cmd, name, args , options }: { cmd: string, name: string, args: Array<string>, options: object }): Promise<NodeJS.ReadableStream>

和女巫中的第三个方法尝试动态调用它们会引发错误

if (typeof firstDeferedCmd == "object" && ( firstDeferedCmd.type === "execute" || firstDeferedCmd.type === "execSpawn" )) {
                ProcessPoolExecutor[firstDeferedCmd.type](firstDeferedCmd); // this line throw the error
}

错误及其自身

无法调用类型缺少调用签名的表达式。键入'（（{{cmd，name}：{cmd：string; name：string;}）=> Promise <{}>）| （（{{cmd，name，args，options} ...'没有兼容的呼叫签名。 ProcessPoolExecutorfirstDeferedCmd.type; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~

Answer 1

问题在于这两个函数具有不同的签名，因此索引操作的结果将是两个签名的并集，根据定义，它们是不可调用的。

您可以使用Function方法call或apply来访问函数（因为它们对于联合中的两个签名都是通用的），因此会丢失所有的缺点类型安全性：

if (typeof firstDeferedCmd == "object" && ( firstDeferedCmd.type === "execute" || firstDeferedCmd.type === "execSpawn" )) {
    ProcessPoolExecutor[firstDeferedCmd.type].call(ProcessPoolExecutor, firstDeferedCmd);
}

您总是可以使用断言来使联合可调用，但这比call更加安全：

if (typeof firstDeferedCmd == "object" && ( firstDeferedCmd.type === "execute" || firstDeferedCmd.type === "execSpawn" )) {
    (ProcessPoolExecutor[firstDeferedCmd.type] as (cmd: IDeferedCmd) => Promise<{stdout: string;stderr: string;}> | Promise<NodeJS.ReadableStream>)(firstDeferedCmd);
}

您还可以使用两项检查来区分两个不同的签名，这实际上暴露了当前设计的问题：

function fn(firstDeferedCmd : IDeferedCmd){
    if (typeof firstDeferedCmd == "object") {
        if(firstDeferedCmd.type === "execute") {
            return ProcessPoolExecutor[firstDeferedCmd.type](firstDeferedCmd);
        }
        if(firstDeferedCmd.type === "execSpawn") {
            if(firstDeferedCmd.args){
                return ProcessPoolExecutor[firstDeferedCmd.type](firstDeferedCmd);  // error since there is no requirement if execSpawn is specified to also specify args
            }
        }
    }
}

我们可以通过更改IDeferedCmd的定义来解决此问题：

type IDeferedCmd = {
    type: "execute",
    cmd: string,
    name: string,
} | {
    type: "execSpawn",
    cmd: string,
    name: string,
    resolve: IResolveFn,
    reject: IRejectFn,
    args: Array<string>,
    options: object


}
function fn(firstDeferedCmd : IDeferedCmd){
    if (typeof firstDeferedCmd == "object") {
        if(firstDeferedCmd.type === "execute") {
            return ProcessPoolExecutor[firstDeferedCmd.type](firstDeferedCmd);
        }
        if(firstDeferedCmd.type === "execSpawn") {
            if(firstDeferedCmd.args){
                return ProcessPoolExecutor[firstDeferedCmd.type](firstDeferedCmd);  // ok now
            }
        }
    }
}

无法调用类型缺少呼叫签名...没有兼容的呼叫签名的表达式

1 个答案: