功能如何运作

Question

I'm a beginner in learning Go, and I'm puzzled by the following two questions:

First:

type S struct{
    a func()
    b func(i int, j float32, k string)
    c *func()
}

func main(){
    s := S{c: &func(){}} // Error: Cannot take the address of `func(){}`
}

In this struct, c *func() is valid, but how can I assigned to it?

Second:
As I know, functions are first class citizens, so I can pass function as a parameter to another function/method, also I can declare a function variable, so, how does a function value works, does it's actually a function pointer?

I read some articles about alignment and padding, I know a interface value take up 16 bytes(64-bit system) because a interface value is composed of data pointer and type pointer, what about function value? I use unsafe.Sizeof(funcValue) and it returns 8, so I guess it's actually a function pointer. Is there any way to prove it(right or wrong)?

Answer 1

If you want to be able to use the address of a variable that points to this function, you'll need to first assign it to a variable.

package main

type S struct {
    a func()
    b func(i int, j float32, k string)
    c *func()
}

func main() {
    c := func() {}
    s := S{c: &c} // No error
}

For more information on the inner workings of functions see the language spec.