Internally, a slice variable is a SliceHeader struct (see https://golang.org/pkg/reflect/#SliceHeader), NOT a pointer to it. Note that len and cap are properties of the SliceHeader struct, NOT of the backing array.
So yes, I made a mistake, the x slice header is copied into z at every iteration. Here's your first example with extra comments to show what happens internally: https://play.golang.org/p/lb3lME5AND Le mardi 14 mars 2017 12:14:20 UTC+1, Cornel Damian a écrit : > > And more, if you assign a slice to another at the beginning will have the > same pointer, until one of them will change the capacity. > > https://play.golang.org/p/BWG5tqayj9 > > On Monday, March 6, 2017 at 12:12:10 AM UTC+2, db0...@gmail.com wrote: >> >> This happens only because z is copied every time, but has nothing to do >> with interfaces. This exhibits the same behavior without interface{}: >> https://play.golang.org/p/C5KoUST4Zn >> >> You could in fact modify the slice's existing content, but not the slice >> itself. For example: >> >> x := make([]int, 1, 5) // we have 1 element >> x[0] = 42 >> for i := 0; i < 4; i++ { >> >> z := x >> >> z[0] = z[0] + 1 >> >> z = append(z, i)) >> >> } >> >> fmt.Println(x[0]) // would print 46 >> fmt.Println(len(x) // still 1 >> >> >> Well, unless you move z's declaration out of the loop as Jan suggested. >> >> I'd recommend reading >> https://blog.golang.org/go-slices-usage-and-internals (manipulating >> slice values was not obvious to me until I read this). >> >> Le jeudi 2 mars 2017 15:23:21 UTC+1, James Bardin a écrit : >>> >>> All assignments are a copy, so there's no way to modify a slice value >>> that is in an interface{} >>> >>> Just like if this were a function argument, you will need a pointer in >>> order to modify the value. >>> https://play.golang.org/p/kOdXUCiT_F >>> >>> >>> >>> On Thursday, March 2, 2017 at 9:01:48 AM UTC-5, Cornel Damian wrote: >>>> >>>> If you look where the slice is printed you will see that the data is >>>> missing. In the working example from me the data is there. >>>> And even so, your example doesn't help me, what i've set there is just >>>> for example, i my code each time i add data to the slice i must first cast >>>> it. >>>> >>>> On Thursday, March 2, 2017 at 3:56:58 PM UTC+2, Jan Mercl wrote: >>>>> >>>>> On Thu, Mar 2, 2017 at 2:46 PM <bar...@gmail.com> wrote: >>>>> >>>>> > Can somebody explain me why? >>>>> >>>>> Did you mean https://play.golang.org/p/GUVZBUQlEj ? >>>>> >>>>> -- >>>>> >>>>> -j >>>>> >>>> -- 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. For more options, visit https://groups.google.com/d/optout.
