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cjdb ldionne • Quuxplusone - Group Reviewers
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- rG40d6d2c49dd1: [libcxx][ranges] Add `ranges::iter_swap`.
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libcxx/include/__iterator/iter_swap.h | ||
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10–11 | s/SWAP/ITER_SWAP/g | |
14–15 | alphabetize plz | |
45–53 | Do we have any sense of whether the Standard intends this unqualified iter_move to refer to std::ranges::iter_move (which is what it currently refers to in this PR, IIUC) or to an ADL iter_move (which is what would make more sense IMHO IIUC)? | |
61 | Here and line 80, I suggest removing the cast to (void). IIUC, the reason it's there in https://eel.is/c++draft/iterator.cust.swap#4.1 is to make the "expression-equivalent-to" part work out to the correct type. | |
76–77 | This should say indirectly_movable_storable<_T1&&, _T2&&>, right? because the type of E1 is not _T1 but rather _T1&&? | |
81 | Here, __iter_exchange_move needs to be ADL-proofed — but actually, I strongly suggest that you just inline its body right here (and inline its noexcept-specification on line 78). Yes I know the Standard factors it out; but it's used only once and the factoring-out doesn't seem to do anything but make the code longer (both in the Standard and in libc++). | |
libcxx/test/std/iterators/iterator.requirements/iterator.cust/iterator.cust.swap.pass.cpp | ||
25 | Has this been done in other tests already? If I'd seen it, I'd say why are you adding the &. | |
31 | nit: explicit plz | |
33 | ||
38–42 | Here and line 54: I'm worried that your implementation of this function is unnecessary and/or indistinguishable from the default ranges::swap, which means you're not actually testing that it's called. How about replacing these implementations with friend constexpr void iter_swap(HasIterSwap& a, HasIterSwap& b) { called1 = true; } friend constexpr void iter_swap(HasIterSwap& a, bool& b) { called2 = true; } and then writing tests that assert(called1 && !called2) (or whatever you expect to happen). | |
85 | Yes — ranges::iter_swap(++i, ++j) is supposed to increment i only once, not twice. | |
156 | It seems like this is testing the order in which std::swap performs its moves — is that right? If so, I don't think it belongs in libcxx/test/std/ at all. Ditto throughout. | |
libcxx/test/std/iterators/iterator.requirements/iterator.cust/unqualified_lookup_wrapper.h | ||
75 | int moves() const { return moves_; } :) |
libcxx/include/__iterator/iter_swap.h | ||
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61 | I'm slightly against removing the void cast, basically to make sure a case like ensureVoidCast works below. | |
76–77 | This is my bad for naming these _T1 and _T2 so when I read the standard wording, my brain thought it meant to just use the template params (which don't exist in the wording). I think you're right. | |
libcxx/test/std/iterators/iterator.requirements/iterator.cust/iterator.cust.swap.pass.cpp | ||
156 | Hmm, I see what you're saying with L155 specifically. And we probably don't really need this test (or maybe a better test would be arr[0].moves() + arr[1].moves() == 3.
Where else do you see this? |
libcxx/include/__iterator/iter_swap.h | ||
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76–77 |
So all of these trait checks should be using e.g. indirectly_movable_storable<remove_reference_t<_T1>, remove_reference_t<_T2>>? Blech. OK. | |
libcxx/test/std/iterators/iterator.requirements/iterator.cust/iterator.cust.swap.pass.cpp | ||
156 | At least lines 159, 162, 165, 168, 171, 174, 177. |
Some initial feedback, will give the tests a more in-depth review in a day or so.
libcxx/include/__iterator/iter_swap.h | ||
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40–43 | ||
56–57 | ||
61 | I would prefer it if ranges::iter_swap didn't randomly cause people to want to enable -Wno-unused-result. Let's keep the cast to void. | |
64–66 | I'll leave the last overload as an exercise. |
libcxx/include/__iterator/iter_swap.h | ||
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61 |
+1 I'm going to leave it. (I don't see any way it hurts to have it, but I can see ways it helps.) | |
64–66 | When I've done this in other places, I've been asked to change it to use requires, and in this case (and especially below) I think it might be clearer than trying to fit it into the template. | |
76–77 |
I think they can actually just be _T1 and _T2 (no remove_reference_t), right? | |
79 | You're right. I thought __iter_exchange_move would take care of this, but it only checks one of the assignment operators, not the other. | |
libcxx/test/std/iterators/iterator.requirements/iterator.cust/iterator.cust.swap.pass.cpp | ||
156 |
These are just checking that the values of the array buff are swapped. I think this is exactly what we want to be checking. |
libcxx/include/__iterator/iter_swap.h | ||
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76–77 | I'm not sure I have the correct words to describe what I'm thinking here but won't the && in _T1&& "eat" the reference part of the reference type? |
libcxx/include/__iterator/iter_swap.h | ||
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40–43 | In other PRs I've been asked to put the !__unqualified_iter_swap part in the requires clause. I also like this better because then the concept is more composable (rather than only being useful in one place). | |
56–57 | This is a bit more confusing imho. If you feel strongly I'll change it, though. | |
64–66 | I'm going to leave this and mark it as resolved. | |
76–77 |
@Quuxplusone ping, does this make any sense? | |
81 | That's not a bad idea, I have to add a move for __old, but I think that's alright. | |
libcxx/test/std/iterators/iterator.requirements/iterator.cust/iterator.cust.swap.pass.cpp | ||
38–42 | Updated to have something similar to this. Let me know what you think. For the record: this isn't really meant to test that we use the correct overload, though. I was just testing that it calls "the overload" it didn't really cross my mind that there would be any way for us to even call the bool& overload with an argument of type HasIterSwap. Anyway, I think it is a good idea to not have this just behave like an assignment operator or default swap impl. | |
85 | Interesting, OK, thanks for explaining. |
I'm unlikely to have any further comments on this, but also don't think I should count as "accepting" it, since I've mainly done superficial stuff and @tcanens had some pretty significant standardese issues (which have probably been dealt with now but I'm not claiming I'm sure of that). I'll let someone-else be the final approver.
libcxx/include/__iterator/iter_swap.h | ||
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74 | Just *_VSTD::forward<_T1>(__x) = _VSTD::move(__old); — no need to cast to void here. | |
76–77 | No; reference collapsing means that when T is int&, T&& is int& (not int&&). | |
libcxx/test/std/iterators/iterator.requirements/iterator.cust/iterator.cust.swap.pass.cpp | ||
142 | This is the only place you test std::ranges::iter_swap(lvalue, lvalue). Please expand the tests below to test them also with lvalues of type HasRangesSwapWrapper, A*, etc., at least enough to hit each different overload of iter_swap once with at least one lvalue. You never test std::ranges::iter_swap(lvalue, rvalue) or std::ranges::iter_swap(rvalue, lvalue), but I don't think those need testing, as long as you hit the (lvalue, lvalue) cases. | |
libcxx/test/std/iterators/iterator.requirements/iterator.cust/unqualified_lookup_wrapper.h | ||
70–71 | move_tracker(const move_tracker&) = delete; move_tracker& operator=(const move_tracker&) = delete; (Deleted functions don't need constexpr.) | |
75 | moves() still doesn't need noexcept. |
libcxx/test/std/iterators/iterator.requirements/iterator.cust/iterator.cust.swap.pass.cpp | ||
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142 | OK. Added a few more lvalue tests to cover the remaining two overloads. | |
libcxx/test/std/iterators/iterator.requirements/iterator.cust/unqualified_lookup_wrapper.h | ||
75 | I think it makes sense to leave the constexpr in this case. This is a sort of general utility. |
libcxx/include/__iterator/iter_swap.h | ||
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43 | I think it would be more in-line with what we usually do to say swappable_with<iter_reference_t<_T1>, iter_reference_t<_T2>> instead. WDYT? As written, I think this is slightly incorrect (but I'm not sure it's possible to notice the difference). The Standard talks about the "reference type of E1 and E2", which is *declval<_T1&&>(), not *declval<_T1>(). But regardless, I think we can just switch to iter_reference_t<_T1> unless there's a problem with that I'm not seeing. | |
56–57 | Agreed, I would definitely keep as-is. | |
69–71 | I don't see how to do better, but it's awful to have to duplicate the body like that. |
libcxx/include/__iterator/iter_swap.h | ||
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43 | Hmm, trying to come up with an example where this doesn't work. I think it's actually 100% valid because indirectly_readable enforces that *in == iter_reference_t: { *in } -> std::same_as<std::iter_reference_t<In>>; So, I'll do that. | |
69–71 | I agree. We should really have a noexcept(auto). This wouldn't be too hard to add to clang, and then we could just let GCC users have worse codegen... |
LGTM with my comments applied.
libcxx/include/__iterator/iter_swap.h | ||
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69–71 | If only that's how things worked 😅 | |
libcxx/test/std/iterators/iterator.requirements/iterator.cust/iterator.cust.swap.pass.cpp | ||
27 | Based on http://eel.is/c++draft/customization.point.object#2, I would just do std::semiregular<std::remove_cv_t<IterSwapT>>. | |
139 | Minor thing: I like to split test different test cases by enclosing them in a different scope. It makes it easier to see that they are different test cases and that they don't share anything between themselves. So I'd do: { int value1 = 0; int value2 = 0; HasIterSwap a(value1), b(value2); std::ranges::iter_swap(a, b); assert(value1 == 1 && value2 == 1); } { int value1 = 0; int value2 = 0; HasRangesSwap c(value1), d(value2); HasRangesSwapWrapper cWrapper(c), dWrapper(d); std::ranges::iter_swap(cWrapper, dWrapper); assert(value1 == 1 && value2 == 1); } // etc... |
I'll properly review this tonight, but I don't suspect I'll have much more to add now.
libcxx/include/__iterator/iter_swap.h | ||
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56–57 | FYI: we're going to be doing this in a lot of algorithms, and it's definitely part of the design of concepts. |
Rebase off main.
This now includes two commits. That's intentional so the CI passes (for some reaosn it was failing to apply the patch before).
s/SWAP/ITER_SWAP/g