Looking again, the second part of my question was wrong (it is a call
to `mapiterkey` and then `mapiterelem` in `Value`).
The code for Key and Value are almost identical, so the question
whether to send a change boils down whether the similarity between the
two is a benefit or a cost. I'm actually leaning towards the similarity
being a benefit and one that would be broken by retaining the value.
Dan
On Tue, 2020-06-30 at 19:24 -0700, Ian Lance Taylor wrote:
> On Tue, Jun 30, 2020 at 6:39 PM 'Dan Kortschak' via golang-nuts
> wrote:
> >
> > Is there a reason not to retain the returned value from
> > `mapiterkey` on
> > line 1243 of reflect/value.go[1] for use on line 1249[2].
> >
> > ```
> > // Key returns the key of the iterator's current map entry.
> > func (it *MapIter) Key() Value {
> > if it.it == nil {
> > panic("MapIter.Key called before Next")
> > }
> > if mapiterkey(it.it) == nil { //L1243
> > panic("MapIter.Key called on exhausted iterator")
> > }
> >
> > t := (*mapType)(unsafe.Pointer(it.m.typ))
> > ktype := t.key
> > return copyVal(ktype, it.m.flag.ro()|flag(ktype.Kind()),
> > mapiterkey(it.it)) // L1249
> > }
> > ```
> >
> > The same question applies to `*MapIter.Value` method just below
> > `Key`.
>
> I don't think there is any reason to call the function twice. The
> value could be retained.
>
> I think the functionswill be inlined, so it probably won't make any
> performance difference, but it might be a little clearer.
>
> Ian
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