[PATCH] D49317: Move __construct_forward (etc.) out of std::allocator_traits.

[Arthur O'Dwyer via Phabricator via cfe-commits]

Quuxplusone added inline comments.


================
Comment at: include/vector:298
+__copy_construct_forward(_Alloc& __a, _Iter __begin1, _Iter __end1,
+                         _Ptr& __begin2, _CopyViaMemcpy)
+{
----------------
vsapsai wrote:
> Why does this function use `_CopyViaMemcpy` and not `false_type` like other functions?
Oops, that's totally cruft left over from an earlier revision. Fixed!


================
Comment at: include/vector:300
+{
+    using _Alloc_traits = allocator_traits<_Alloc>;
+    for (; __begin1 != __end1; ++__begin1, (void)++__begin2)
----------------
vsapsai wrote:
> Have you checked why `using` is accepted in C++03 mode? The tests are passing but I expected a compiler warning and didn't investigate further.
I talked with Glen Fernandes about this on Slack the other day. I think the deal is that `make check-cxx` runs only the `-std=c++2a` tests, and if you want `-std=c++03` you have to run them manually with `llvm-lit --param=-std=c++03 -sv path/to/tests`. Which of course I didn't do. :)
If there's a more foolproof way of automatically testing libc++ in *all* compiler modes, I'd like to know about it.

Fixed!


================
Comment at: include/vector:542
+template<class _Tp, class _Allocator>
+struct __vector_copy_via_memcpy : integral_constant<bool,
+    (is_same<_Allocator, allocator<_Tp> >::value || !__has_construct<_Allocator, _Tp*, _Tp>::value) &&
----------------
vsapsai wrote:
> I think the name `__vector_constructable_via_memcpy` better reflects the meaning. It detects cases when individual element construction can be safely replaced with memcpy, so it feels more about construct than about copy. And `copy_via_memcpy` is too imperative as for me, not really conveying it has boolean semantic.
> `copy_via_memcpy` is too imperative for me

I see your point. However, for background... in my other branch, this trait is joined by two companions:
```
struct __vector_relocate_via_memcpy
struct __vector_destroy_via_noop
```
So I'd like a naming scheme that fits all three use-cases comfortably.

How about just adding the word "should"?  `__vector_should_construct_via_memcpy`, `__vector_should_destroy_via_noop`, etc?  Would that sufficiently address the "too imperative" issue?


================
Comment at: include/vector:1015
 {
+    typedef typename __vector_copy_via_memcpy<_Tp, _Allocator>::type __copy_via_memcpy;
     __annotate_delete();
----------------
vsapsai wrote:
> It's not immediately obvious why there is no check like `is_same<_ForwardIterator, _Tp*>` here. My guess is that we are using variables like `this->__end_`, `v.__begin_` that we know are pointers. Don't think it's really a problem and not suggesting any changes, decided to mention it's a little bit tricky to understand.
Your guess is 100% correct, AFAIK. All we're doing here is copying from one `__split_buffer` to another, so both sides are always a contiguous range.


Repository:
  rCXX libc++

https://reviews.llvm.org/D49317