[cfe-dev] [libc++] use of allocator_traits

Marshall Clow via cfe-dev cfe-dev at lists.llvm.org
Fri Apr 13 14:34:26 PDT 2018

On Fri, Apr 13, 2018 at 1:23 PM, Eric Fiselier via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> On Thu, Apr 12, 2018 at 3:20 AM, Axel Naumann via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>> Hi,
>> I'm confused by libc++'s use of allocator_traits, for instance in
>> vector:898:
>>     __alloc_traits::__construct_backward(this->__alloc(),
>> this->__begin_, this->__end_, __v.__begin_);
>> The standard seems to not require the existence of a member called
>> __construct_backward. Seemingly standard-conforming, user provided
>> specializations of this trait (for a user provided allocator) thus fail
>> to compile.
>> Am I misinterpreting allocator_trait as a customization point?
> I would have thought so, because my understanding was that the allocator
> was the customization point, where as allocator_traits was the interface
> used
> to deal with the custom allocator.
> However, the standard seems to disagree with me, noting that users
> may specialize `allocator_traits`.
interesting. :-(

Please open a bug at bugs.llvm.org, and I'll look into it when I get back
from the LLVM devcon.

-- Marshall
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