func关键字后有两个函数名-这是什么？

Question

How to understand the last function? Why do we use different function names after func declaration? How to use those function? Using it like shown in the main function is wrong.

package main

import (
    "fmt"
)

func main() {
    fmt.Println(incrementer()) //error
}

func incrementer() func() int { //what is it?!
    i := 0
    return func() int {
        i++
        return i
    }
}

Answer 1

Simply, since incrementer() returns a function, the function that it returns must be called as well. You can do so like this:

functionFoo := incrementer()
fmt.Println(functionFoo())

Or this shorthanded way:

fmt.Println(incrementer()())

Which achieves the same thing, you just immediately execute the function that incrementer() returns.