append() in Go is destructive against how it looks on the code.

If the capacity of s is not large enough to fit the additional values, append allocates a new, sufficiently large underlying array that fits both the existing slice elements and the additional values. Otherwise, append re-uses the underlying array.

package main

import "fmt"

func main() {
	test := []int{1, 2, 3, 4, 5, 6}//cap(6)
	fmt.Printf("address of test %p\n", test)
	test = append(test, 7)//cap(12)
//	fmt.Printf("address of test %p\n", test)
	
	
    test2 := append(test, []int{7,8,9}...)//len() cap(12)
	fmt.Println(test)
	fmt.Println(test2)
    test2[0] = -1
	fmt.Println(test)
	fmt.Println(test2)
	fmt.Printf("length of test = %v, length of test2 = %v\n", len(test), len(test2))
	fmt.Printf("capacity of test = %v, capacity of test2 = %v\n", cap(test), cap(test2))
	
	test = append(test, 10)//cap(12)
	fmt.Println(test)
	fmt.Println(test2)
	fmt.Printf("address of test %p\n", test)
	fmt.Printf("address of test2 %p\n", test2)
//	fmt.Printf("address of test %p add of test2 %p \n", &test, &test2)
}

Links

The Go Programming Language Specification - The Go Programming Language

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