不同类型的指针有什么区别？

A pointer references a location in memory. Actually all memory addresses have the same type independently of the variable type as far as I understand.

Instead of using different pointer type (*int, *string etc..), is this possible using only one type (var p pointer) for all the pointer types?

What is the difference between different pointer types?

package main

import "fmt"

func main() {
    i := 5
    s := "abc"

    var pi *int      // alternatively var pi pointer
    var ps *string   // alternatively var ps pointer 

    pi = &i
    ps = &s

    fmt.Printf("%p %p", pi, ps)  // result is 0x1040e0f8 0x1040a120
}

is this possible using only one type for all the pointer types?

Yes, that is pretty much how C works. Unfortunately, that makes the language dangerous. Say you have an array of 10 bytes. If you JUST pass the pointer, the other code won't know how many bytes it's safe to access. That leads to all kinds of buffer overflow errors. (i.e. HeartBleed)

In Go, they pointer knows the type of the thing it points to, so it can prevent your code from having buffer overflow problems all the time.

You can do what you want, but only by using the Unsafe package. As the name suggests, that is a very dangerous thing to do.

Perhaps if you post what you are ACTUALLY trying to do, people can help you. Using unsafe pointers is not the only way to write performant code.

The type system in Go is designed to prevent memory errors relating to pointers. This allows programmers to have enough control to manipulate objects in memory while Allowing the garbage collector top cop moody of the heavy lifting.
If you need to manually memory and convert pointer types you can use the unsafe package.