在golang中，我推迟了一个函数返回函数，命令是什么

Question

I write the follow code

package main

import "fmt"

func main() {
    defer func() func() {
        fmt.Println("start")
        return func() {
            fmt.Println("end")
        }

    }()()
    fmt.Println("aaaa")
    return

}

and I except output is aaaa start end

but actual output is start aaaa end

I can't understand why output "start" before "aaaa"

Answer 1

The specification says:

Each time a "defer" statement executes, the function value and parameters to the call are evaluated as usual and saved anew but the actual function is not invoked.

The deferred function call is the last () in the defer statement. The expression returning the function value is evaluated at the time of the defer statement.