Add 'operator==' for 'basic_collection_iterator'

[Alex Denisov via llvm-commits]

> It really shouldn't be defining itself as a forward iterator. I think we should just make it an input iterator

Makes sense. I also looked at specification (§24.2.3, §24.2.5): the iterator doesn’t conform some requirements described there (e.g. multi-pass guarantee).

> and assert that the entries are the same if the bases are the same.

How do you want express the assertion? Do you mean semantic assertion e.g.: 'X == Y iff X.Base == Y.Base’ or something different?
--
AlexDenisov
Software Engineer, http://lowlevelbits.org

> On 18 Dec 2015, at 19:22, Jordan Rose <jordan_rose at apple.com> wrote:
> 
> 
>> On Dec 18, 2015, at 5:49 , Alexey Denisov <1101.debian at gmail.com> wrote:
>> 
>>> Ha, I was still thinking something simpler.
>> 
>> I came up with the same solution when I woke up next morning :-D
>> 
>>> EXPECT_FALSE(Begin == std::next(Begin));
>>> EXPECT_FALSE(std::next(Begin) == Begin);
>> 
>> I have faced an issue with such tests. std::next in the case of SequenceNode mutates value in-place, so that iterators are equal.
>> But it could be tested using some other BaseT, not a SequenceNode. I also realised it afterwards.
>> 
>>> InputIterators don't actually guarantee that this is valid, so we don't have to implement it, but I think we should do it just so other people don't get bitten. There's not much reason not to.
> 
> I looked at basic_collection_iterator again. It really shouldn't be defining itself as a forward iterator. I think we should just make it an input iterator and assert that the entries are the same if the bases are the same.
> 
> Jordan

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