On Tue, Feb 11, 2020 at 3:55 PM 'Kevin Regan' via golang-nuts
<golang-nuts@googlegroups.com> wrote:
>
> Would something like this work:
>
> m1 := make(map[string]string)
> m2 := m1
>
> if &m1 == &m2 {
> ...
> }
That would do something but it's not a particularly interesting
property. I'm not sure what you are trying to check.
If you want to test whether two variables of map type have equality of
reference--whether both variables refer to the same map--you can write
reflect.Value(m1).Pointer() == reflect.Value(m2).Pointer()
Ian
> On Tue, Feb 11, 2020 at 5:50 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...
>>
>>
>> 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?
>>>
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