[PATCH] RFC: fail-fast iterators for DenseMap

[Chandler Carruth]

On Mon, Mar 2, 2015 at 8:20 PM, Duncan P. N. Exon Smith <
dexonsmith at apple.com> wrote:

> > On 2015 Mar 2, at 20:12, Sanjoy Das <sanjoy at playingwithpointers.com>
> wrote:
> >
> >> Comparing two default constructed iterators should be valid, but
> >> I don't understand how your patch affects that operation.  Am I
> >> missing something obvious?
> >
> > In the current implementation, default constructed iterators have a
> > nullptr epoch address, so looking up their epoch segfaults.
>
> What I don't see is where you change the comparison of `DenseMapIterator`
> to depend on the epoch.  AFAICT, you only modified `++`, `*`, and `->`,
> none of which should be called from `==` or `!=`.
>
> >
> > In any case, the fix should be easy; I just wanted a clarification on
> > what the intended semantics are.
> >
>
> For `==` and `!=, you shouldn't worry about whether the handle is in sync
> with the debug base -- if anything, you should just check that the two
> handles are pointing at the same debug base (and have the same epoch as
> each other).  (But I still don't see how you've modified `==` or `!=`.)


The comparison operators call operator->
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