Add 'operator==' for 'basic_collection_iterator'

[Alex Denisov via llvm-commits]

So I changed iterator tag to input_iterator and re-implemented equality operators.

Now it looks trivial:

bool operator==(const basic_collection_iterator &Other) const {
  return Base == Other.Base;
}

See the whole patch:

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--
AlexDenisov
Software Engineer, http://lowlevelbits.org

> On 18 Dec 2015, at 21:05, Alex Denisov <1101.debian at gmail.com> wrote:
> 
>> 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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