Can you write a concept for ContiguousIterator?

Question

I know there is concept for ContiguousIterator in words specification sense, but I wonder if it can be written using C++20/C++17 Concepts TS syntax.

My problem with this is that unlike RandomAccessIterator ContiguousIterator requires not just some operations like it+123 to work, but depends on runtime result of that operation.

score 2 · Accepted Answer · answered Dec 09 '17 at 04:09

2

No you cannot, not without a traits class or other helper, where types opt-in to being contiguous.

answered Dec 09 '17 at 04:09

Yakk - Adam Nevraumont

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I don't know... isn't the definition for some `ContiguousIterator i` that `&*(i+1) == &*i + 1`?? – Massa Dec 14 '17 at 18:38
1

@massa How do you check that at compile time? Over all instances of the type? – Yakk - Adam Nevraumont Dec 14 '17 at 19:19
I don't have an answer, and I have to concede that it may be impossible... If I can grasp it, I'll come back here :-/ – Massa Dec 14 '17 at 19:21

score 2 · Answer 2 · answered Dec 09 '17 at 07:08

Your problem is currently unsolvable. The committee is considering what to do about deducing contiguous memory access. The flub is that iterator_category is not a trait (although it resides in iterator_traits); It is an ad-hoc type. It cannot be subtyped without breaking existing code. (Beginner mistake, eh what?) The Committee has recognized the mess. This recent discussion tells all -> How to deduce contiguous memory from iterator

Can you write a concept for ContiguousIterator?

2 Answers2