为什么不能在分配中使用（func（string）类型）作为func（interface {}）类型

Please first have a look at the code below.

package main

import "fmt"

type InterfaceFunc func(interface{})
type StringFunc func(string)

func stringFunc(s string) {
    fmt.Printf("%v", s)
}

func interfaceFunc(i interface{}) {
    fmt.Printf("%v", i)
}

func main() {
    var i = interfaceFunc
    var s = stringFunc

    i = s // I would like someone to explain why this can't be done exactly.
}

Run at https://play.golang.org/p/16cE4O3eb95

Why an InterfaceFunc can't hold a StringFunc while an interface{} can hold a string.

You can not do s = i or i = s, and the reason is both functions are of different type (different signatures), you can not just assign one type with another in golang.

Also type InterfaceFunc func(interface{}) type StringFunc func(string) are sitting there doing nothing.