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无法调用其类型缺少调用签名的表达式…没有兼容的调用签名

types typescript javascript

Amit Wagner · 技术社区 · 6 年前

我有个错误

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

在我的一个方法上,我想不出怎么解决它。我看过这个链接 cannot-invoke-an-expression-whose-type-lacks-a-call-signature

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


}

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>

还有第三个方法,在这个方法中,错误是从尝试动态调用它们时抛出的

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

以及它本身的错误

ProcessPoolExecutorfirstDeferedCmd.type; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

1 回复 | 直到 6 年前

Titian Cernicova-Dragomir 6 年前

问题是这两个函数有不同的签名,因此索引操作的结果将是两个签名的联合,根据定义,这两个签名是不可调用的。

Function 方法 call 或 apply 可访问(因为它们对联合体中的两个签名都是通用的)来调用函数,但缺点是会丢失所有类型安全性:

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

您可以始终使用断言使联合可调用,但这样做并不安全 :

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);
}

您还可以使用两个检查来指定两个不同的签名,这实际上暴露了当前设计的一个问题:

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
            }
        }
    }
}

我们可以通过改变 IDeferedCmd

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
            }
        }
    }
}