On Mon, Feb 17, 2020 at 11:18 AM <kloste...@gmail.com> wrote: > Out of curiosity: Could you please tell when calling methods on nil > pointers is useful? >
In general, linked datastructures - like linked lists or trees. As a somewhat trivial example, consider this: https://play.golang.org/p/Y-4aSVLzEFO Interpreting a nil-pointer as "an empty tree" makes a lot of the traversal-algorithms easier to express. I also have an internal package that wraps the openat/mkdirat/linkat/… class of syscalls, to make it possible to still read/write a directory that has been bind-mounted over. It uses a struct to encapsulate the file-descriptor of that directory, which is used as a pointer to keep track of whether it has been closed and such. It also interprets a nil-pointer as "relative to the current directory" (it uses AT_FDCWD). I could, of course, also use the zero-value of that struct for that (in fact, I do as well), but as there is a meaningful way to interpret a nil-pointer, there's no harm in doing so as well. In general, it's of course never *necessary* to interpret a nil-pointer a specific way. But it does sometimes make things easier to express or nicer to use. BTW, as far as slices are concerned: They behave strikingly similar to maps, as far as the zero-value is concerned - in that all read-operations work just fine on both a nil-map and a nil-slice, it's just that write-operations panic (and again, in both cases). The main difference between them is that *non*-nil maps behave very differently. We don't tend to notice the "uselessness" of nil-slices in general, though, because we tend to either assume a certain size for them (in which case they can't be nil) or we check the length beforehand (just like checking if a map is nil) when writing to them. i.e. the read-operations are far more common with slices and we find the idea of "checking" their nil-ness via ranging over them or explicitly checking their len somewhat more natural. -- 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/CAEkBMfHAfA97soJy1iXea1H7Bkv_VO%3D43cLY96zi%2BZ7R0a%3DbTQ%40mail.gmail.com.
