libc++: First cut at <dynarray>

Marshall Clow mclow.lists at
Mon Sep 9 15:32:59 PDT 2013

On Sep 9, 2013, at 11:59 AM, Richard Smith <richard at> wrote:
> On Mon, Sep 9, 2013 at 9:06 AM, Marshall Clow <mclow.lists at> wrote:
> <dynarray> See
> Open Issues:
> 1) This includes <tuple> because that's where __uses_alloc_ctor lives. I'm thinking that __uses_alloc_ctor should be hoisted into a common header. Maybe __functional_base.
> 2) This includes a general implementation of user-allocator construction (named __user_alloc_construct). This should probably be hoisted as well; and possibly the code in scoped_allocator can be reworked to use it (if it simplifies things).
> 3) There's no support for stack allocations at present; that requires compiler support. I'm working with some people on getting that into clang.
> 4) There's an awful lot of duplication in the (many, many) constructors.
> It's not obvious to me that the behavior of max_size is correct.

What do you suggest it return?
It returns the current size of the array - and that's the max size that array can be.
[ This is the same behavior as std::array, btw ]

> To my reading, __allocate is required to throw std::bad_array_length if the multiplication overflows.

Yes. Nice catch.
This led me down a bit of a rathole, b/c libc++ hasn't implemented std::bad_array_length yet.
I'll have a (separate) patch for that up in a bit.

> Your reinterpret_casts from void* to (const) _Tp* could be static_casts.


> The constructor overloads look... horribly broken. This won't work:
>   std::dynarray<long> arr(20, 0);
> ... because it picks the (size_t, const _Alloc&) constructor, not the (size_t, const value_type&) constructor. Is there an LWG issue for that?

No, actually, it picks the right version; but I've added that exact case to the test suite.

I wouldn't mind some SFINAE here for the "Allocator" routines, though.
I need a good "is_allocator" template metafunction.

Thanks for the review.

-- Marshall

Marshall Clow     Idio Software   <mailto:mclow.lists at>

A.D. 1517: Martin Luther nails his 95 Theses to the church door and is promptly moderated down to (-1, Flamebait).
        -- Yu Suzuki

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