I have a lot of constraints in the issue I am encountering, so I have greatly simplified it to this unnatural code containing the following stuff:

• A struct named Rect
• rA and rB both of which point to a new Rect object
• r1 and r2, which are interfaces containing rA and rB
• r1Adr and r2Adr, which are interfaces containing the addresses of rA and rB

I want to do rA = rB without being allowed to reference rA or rB after declaring my variables.

(Note: you would think it would be easy, and that you would just do *r1.(*Rect) = *r2.(*Rect). However, the issue with this approach is that it does not point rA to rB's Rect object—it merely clones the values of rB's Rect to rA's Rect. So, I instead have to dereference a pointer to rA (r1Adr) and assign it to rB so that rA points to the same Rect object as rB.)

Below is my attempt at doing so:

type Rect struct {
    width int
}

func main() {
    rA := new(Rect)
    rB := new(Rect)

    var r1, r2, r1Adr, r2Adr any
    r1 = rA
    r2 = rB
    r1Adr = &rA
    r2Adr = &rB

    *r1Adr.(**Rect) = *r2Adr.(**Rect)

    // print the address of each Rect object being stored
    fmt.Printf("%p, %p, %p, %p, %p, %p", rA, rB, r1, r2, *r1Adr.(**Rect), *r2Adr.(**Rect))
}

0xc00001c038, 0xc00001c038, 0xc00001c030, 0xc00001c038, 0xc00001c038, 0xc00001c038

PLAYGROUND: https://go.dev/play/p/VnQwx6V7DNa

As you can see from the output, rA is correctly updating to rB, and r1Adr and r2Adr are reflecting this perfectly. However, r1's rA is not updating to rB, which we know because its output is different. Why is this? If rA is being updated to rB, and if r1 stores rA, then how is it that the rA pointed to by r1 is not updating to rB?

Any insight as to how I can initialize r1 in such a way (without changing it from an interface) that it properly updates after doing *r1Adr.(**Rect) = *r2Adr.(**Rect) would be greatly appreciated.

CodePudding user response：

rA and rB are two pointers pointing to separate objects, A and B.

r1 is an interface pointing to A, and r2 is an interface pointing to B.

r1Addr is an interface pointing to &rA, and r2Addris an interface pointing to&rB`.

Thus, when you update the contents of r1Addr1, you make rA point to rB.

However, r1 and r2 are still pointing to A and B. They did not change.