[PATCH] RFC: fail-fast iterators for DenseMap

[Sanjoy Das]

As far as I can tell, DeclContext::lookups [1] tries to create an
empty range using two default constructed
DeclContext::all_lookups_iterator[2].
DeclContext::all_lookups_iterator contains DenseMapIterators.

[1]: https://github.com/llvm-mirror/clang/blob/master/include/clang/AST/DeclLookups.h#L81
[2]: https://github.com/llvm-mirror/clang/blob/master/include/clang/AST/DeclLookups.h#L35

On Mon, Mar 2, 2015 at 7:21 PM, Daniel Berlin <dberlin at dberlin.org> wrote:
>
>
> On Tue, Mar 3, 2015 at 12:53 PM, Sanjoy Das <sanjoy at playingwithpointers.com>
> wrote:
>>
>> I'm about to revert this because it broke clang.
>>
>> The reason it broke clang is that clang assumes a default constructed
>> DenseMapIterator is comparable with another default constructed
>> DenseMapIterator.
>
>
>
> Where does this happen?
> I'd really like to see an actual example of how this makes sense to do
>
> i have no idea whether it's generally considered "normal" to do this, but
> i'm actually really curious to see a case where it is the right thing to do
> :)
>