相等的指针是否不同？

Question

This code creates two interface variables from the same pointer. The prints demonstrate that they are the same pointer (as opposed to storing copies of s and s2). Yet, the last print says i1 is not the same as i2. Why?

package main
import "fmt"
func main() {
    var s T = &struct{string}{}
    var s2 *struct{string} = s
    var i1 interface{} = s
    var i2 interface{} = s2
    fmt.Println(s)
    s.string = "s is i1"
    fmt.Println(i1)
    s.string = "s is i2"
    fmt.Println(i2)
    fmt.Println(i1==i2)
}

type T *struct{string}

$ go run a.go
&{}
&{s is i1}
&{s is i2}
false

Answer 1

Here's what the Go langauge specification says about comparing interface values:

Two interface values are equal if they have identical dynamic types and equal dynamic values or if both have value nil.

The value in i1 has the named type T. The value in i2 has the anonymous type *struct{string}. Because the two values have different dynamic types, the interface values are not equal.

To see the types, add this line to your program:

fmt.Printf("i1: %T, i2: %T
", i1, i2)

This line will print:

i1: main.T, i2: *struct { string }