Comment by zeeboo

I think I didn't communicate my point clearly. Consider this hypothetical program:

    x := make(map[int]int)
    x[0] = 5
    
    y := &x[0]
    *y = 10
    
    print(x[0]) // 5 or 10?
    
    x[0] = 6
    
    print(*y) // 6 or 10?
    
    // force the map to grow and reallocate the buckets
    for j := 1; j < 100; j++ {
        x[j] = j
    }
    *y = 11
    
    print(x[0]) // 5, 6, 10, or 11?

The crux of the problem is answering what y actually points at: the value in the map bucket, or some freshly allocated value? There are problems with whichever one you pick.

edit: changed the second print to *y instead of x[0]. thanks masklinn for catching this error.