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

Posted 2023-03-13

【中文标题】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

【英文标题】：Cannot invoke an expression whose type lacks a call signature ... has no compatible call signatures

【发布时间】：2019-01-26 06:58:47

【问题描述】：

我得到一个错误

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

在我的一种方法上，我不知道如何解决它。 我看过这个链接cannot-invoke-an-expression-whose-type-lacks-a-call-signature

还有2个，但还是没弄明白

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>

还有第三种方法，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

及其自身的错误

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

【参考方案1】：

问题是这两个函数有不同的签名，所以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。

您可以使用可访问的Function 方法call 或apply（因为它们对联合中的两个签名都是通用的）来调用该函数，但缺点是会失去所有类型安全性：

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

您总是可以只使用断言来使联合可调用，但这并不比call 更安全：

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分离出两个不同的签名，这实际上暴露了您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的定义来解决这个问题：

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