I added a little more to your example to illustrate my email points. https://play.golang.org/p/eT5tKUniC1E
1) stack_array may or may not be on the stack, Go makes that choice. 2) slice := stack_array[:] Doesn't copy the data, it creates a slice structure which wraps it. 3) Next, when you call slice = append(slice, 99), Go will allocate a new backing buffer and copy the initial four values. Now you have a copy. "slice". A slice is just this struct: https://golang.org/src/runtime/slice.go type slice struct { 14 array unsafe.Pointer 15 len int 16 cap int 17 } When you create your initial slice, you get array = stack_array, len = 4, cap = 4. When you append the next element, you get array = <new array>, len=5, cap=5. The first 4 elements will have been copied. -- Marcin On Sat, Apr 18, 2020 at 10:26 AM Miguel D <david.horiami...@gmail.com> wrote: > Hello everyone. > I'm learning the go language and I have some questions regarding the > implementation of slices. > > *$ cat slice_stack.go * > package main > > import "fmt" > > func main() { > stack_array := [4]int{1,2,3,4} > // !- I assume this is on the stack, like a local int[4] would be in > C. > > slice := stack_array[:] // Does this copy the data to the heap? > // or just get a slice to the mem on the > stack? > for i := 0; i<25; i++ { > slice = append(slice, 99) // Does this copy the data to the heap > on first append? > } > > fmt.Println(stack_array) > fmt.Println(slice) > } > > > *$ go run slice_stack.go * > [1 2 3 4] > [1 2 3 4 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 99 > 99 99 99] > > Is it common to get slices to arrays on the stack? Am I wrong when I say > *stack_array* is on the stack? > Thank you. > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/221259d6-8cd2-4f51-b67d-757a0f802e7b%40googlegroups.com > <https://groups.google.com/d/msgid/golang-nuts/221259d6-8cd2-4f51-b67d-757a0f802e7b%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CA%2Bv29Lt%3D8M-cGLQO5SVxzhUkL_-x5OUSiDzX_Cw1%2BgwYVuAwtQ%40mail.gmail.com.
