函数递归

Question

我正在开发一个装饰器来将中间件添加到 AWS lambda，这里是源代码。我在这方面的灵感来自调解器的源代码（具体来说，class link 中的“RequestHandlerWrapperImpl”）。所以我拿了 C# 代码并试图将它传递给 Typescript。简化代码是这样的。


// Used Types
type HandlerDelegate = () => Promise<APIGatewayProxyResult>;
type Handler = (event: APIGatewayProxyEvent) => Promise<APIGatewayProxyResult>
type Middleware = (event: APIGatewayProxyEvent, next: HandlerDelegate) => Promise<APIGatewayProxyResult>;

// Middlewares
const first = (event: APIGatewayProxyEvent, next: HandlerDelegate) =>{
  console.log("first in")
  const response = next();
  console.log("first out")

  return response;
};

const second = (event: APIGatewayProxyEvent, next: HandlerDelegate) =>{
  console.log("second in")
  const response = next();
  console.log("second out")

  return response;
};

// Executable logic
const read = forHandler(async () : Promise<APIGatewayProxyResult> 
      => APIResponse.createSuccess(HttpStatusCode.OK, "handler"))
  .addMiddleware(first)
  .addMiddleware(second)
  .finish;


// finish method

const finish = (event: APIGatewayProxyEvent) : Promise<APIGatewayProxyResult> => {
    let result: HandlerDelegate = () => handler(event);
        
    for (let i = 0; i < middlewares.length; i++) {
        result = () => middlewares[i](event, result);

    }

    return result();
}

预期的日志是这样的：

"first in"
"second in"
"handler"
"second in"
"first in"

但是，这是，直到溢出异常

"second in"
"second in"
"second in"
"second in"
"second in"
"second in"
"second in"
"second in"

谁能解释一下为什么会这样？我认为是因为在

行

result = () => middlewares[i](event, result);

我完全替换了结果变量（在“两侧”）。因此，它不是递归的，而是循环的。另外，我怎样才能让它按预期工作？

Answer 1

解决方案修改了finish函数，改为：

const finish = (event: APIGatewayProxyEvent) : Promise<APIGatewayProxyResult> => {
    let result: HandlerDelegate = () => {
        return handler(event);
    };
        
    for (let i = 0; i < middlewares.length; i++) {
        let resultCallback = result; 
        result = () => {
            return middlewares[i](event, resultCallback);
        };
    }

    return result();
}

有了这个，结果函数就不会被覆盖，我们让管道工作

函数递归

Recursion on function

typescript

recursion