Add 'operator==' for 'basic_collection_iterator'

[Jordan Rose via llvm-commits]

Thanks for the post-holiday ping. Committed to LLVM as r256913. Thanks for the patch!

Jordan

> On Jan 4, 2016, at 22:03 , Alex Denisov <1101.debian at gmail.com> wrote:
> 
> Ping :)
> --
> AlexDenisov
> Software Engineer, http://lowlevelbits.org
> 
>> On 20 Dec 2015, at 10:24, Alex Denisov <1101.debian at gmail.com> wrote:
>> 
>> Here is updated version. Hopefully comment and assert are expressive enough.
>> Also, expressed operator!= as negation of operator==, to not copy-paste assertion.
>> 
>> <basic_collection_iterator_operator_equals.patch>
>> 
>> --
>> AlexDenisov
>> Software Engineer, http://lowlevelbits.org
>> 
>>> On 19 Dec 2015, at 01:33, Jordan Rose <jordan_rose at apple.com> wrote:
>>> 
>>> Yep, that's what I meant, but it needs a comment to explain why it's safe.
>>> 
>>> The assertion I wanted was
>>> 
>>> if (Base && Base == Other.Base)
>>> assert(Base->CurrentEntry == Other->CurrentEntry && "appropriate message here");
>>> 
>>> That'll get trivially compiled out in Release builds, but in Debug builds it will catch any changes to the YAML parser in the future that might break the assumption.
>>> 
>>> Jordan
>>> 
>>>> On Dec 18, 2015, at 13:11, Alex Denisov <1101.debian at gmail.com> wrote:
>>>> 
>>>> 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:
>>>> 
>>>> <basic_collection_iterator_operator_equals.patch>
>>>> --
>>>> 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
>>>>> 
>>>> 
>>> 
>> 
>