On Tue, Feb 11, 2020 at 5:51 AM roger peppe <rogpe...@gmail.com> wrote: > > I believe that the main reason that equality isn't defined on maps (and > slices) is to preserve the future possibility that equality might work at a > whole-value level rather than on a reference level. I suspect that one of > these days a final decision will be made...
I would say that slightly differently. Equality of reference types is ambiguous. Does slice or map equality mean equality of reference or equality of value? Different programs want different choices; neither is obviously correct. So the language doesn't make a choice. Ian > On Mon, 10 Feb 2020 at 23:42, 'Kevin Regan' via golang-nuts > <golang-nuts@googlegroups.com> wrote: >> >> I just ran into this... ...makes me like go a little less. >> >> >> On Tuesday, August 7, 2018 at 6:34:03 AM UTC-7 mi...@daglabs.com wrote: >>> >>> Sorry for bumping a very old thread, but I absolutely disagree with the >>> people stating that this problem is contrived, and I got here from a Google >>> search, so this might be relevant for some people. >>> >>> A very real use-case for reference-comparing maps is when testing .Clone() >>> methods. You want to make sure that the clone is an actual clone, and that >>> all the properties of the cloned object are also a clone, etc. In these >>> cases you want to reference-compare everything. >>> >>> That said, reflect.ValueOf(xxx).Pointer is more than sufficient for this >>> use-case. >>> >>> >>> On Monday, July 15, 2013 at 3:50:01 AM UTC+3, Yi DENG wrote: >>>> >>>> There're always something that is not comparable. You can consider map as >>>> one of this. If you have to check, use the pointer form. >>>> >>>> David >>>> >>>> On Saturday, July 13, 2013 7:35:55 PM UTC+8, Jsor wrote: >>>>> >>>>> I ask for maps because for slices this seems potentially problematic: >>>>> what does "same reference" entail for a slice? Overlapping underlying >>>>> arrays? Same starting pointer regardless of whether their len matches? >>>>> Same start, end, len, and cap? And so on. Though I guess >>>>> "reference-equality" would be pretty well defined for channels. >>>>> >>>>> However, for maps determining "sameness" at a reference level seems like >>>>> a much more well defined question, and a much simpler one to answer. Yet >>>>> I can't figure out a good way to do it. Perhaps with >>>>> reflect.Value.UnsafePointer (would that even work)? Either way, that >>>>> seems like overcomplicating things. The "easiest" way to do it seems to >>>>> be something like this, dreamt up on the go-nuts IRC when I asked this: >>>>> http://play.golang.org/p/6Ffxfx7zBb >>>>> >>>>> But I think we can all agree that that's a rather silly and limited >>>>> solution (and to be fair wasn't suggested in earnest). >>>>> >>>>> I can see why == isn't defined on maps, too many people would likely >>>>> mistake it for a deep equality test (if that was indeed the reason), but >>>>> it seems like there should be some semi-trivial way to see if two map >>>>> variables refer to the same map. Perhaps a need just wasn't seen for such >>>>> an operation? Maybe it's really a more difficult/expensive test than I >>>>> assumed? >> >> -- >> 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/a1f4e265-4523-41be-a67a-f43610fd430a%40googlegroups.com. > > -- > 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/CAJhgacgt5ddXTGEr5nXxS3UCxRqcBkzZcyhYU70jbcejT0r87A%40mail.gmail.com. -- 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/CAOyqgcVNdNHtX4tQu15u7GYUTPy29YPQXsCPibWrdxRmRwUtDQ%40mail.gmail.com.
