Re: [boost] [STL + allocators] Bug?

Subject: Re: [boost] [STL + allocators] Bug?
From: Phil Bouchard (phil_at_[hidden])
Date: 2016-02-18 23:21:16

On 2016-02-18 10:29 PM, Phil Bouchard wrote:
> On 2016-02-18 7:09 PM, Phil Bouchard wrote:
>> On 02/18/2016 06:30 AM, Phil Endecott wrote:
>>> Phil Bouchard wrote:
>>>> I think [std::list etc] should make use of the allocator's specific
>>>> pointer
>>>
>>> In C++03, containers were allowed to assume that allocator::pointer
>>> == value_type*.  This is not true since C++11, where it should use
>>> allocator::pointer via allocator_traits.
>>>
>>> A subtlety is that in the code you posted you're dealing with node
>>> pointers, not value_type pointers.  I'm not sure what's going on there.
>>> My first thought was that you were looking at a pre-11 version of
>>> libstdc++, but I see a #if that suggests otherwise.  Maybe others
>>> can comment.
>>>
>>> You might like to look at how Boost.Container works.  It should use
>>> allocator::pointer even on C++03.
>>>
>>> Note that trying to use a smart pointer for allocator::pointer is
>>> unlikely to work in general, e.g. you can't use shared_ptr, because
>>> the semantics are not what the container expects.  The most common
>>> use for redefining allocator::pointer that I've seen is to store
>>> offset in memory-mapped files and similar.
>>
>> Thanks for your input...  I am trying out boost::container::... right
>> now and it is not a trivial task to use a smart pointers inside
>> containers but I think it is possible.
>>
>> I saw functions like to_raw_pointer() were user before calling the
>> allocator's constructors & destructors... I believe this should be
>> cleaned up sooner or later but for now I think I can survive by
>> overloading only the allocate & deallocate functions.
>
> I managed to make it compile with MSVC 2015 with a smart pointer inside
> containers:
>
> template <typename T, typename UserPool = system_pool<system_pool_tag,
> sizeof(char)> >
>      class block_allocator
>      {
>          typedef T                               element_type;
>
>      public:
>          typedef element_type                    value_type;
>          typedef size_t                          size_type;
>          typedef ptrdiff_t                       difference_type;
>          typedef block_ptr<element_type>         pointer;
>          typedef block_ptr<const element_type>   const_pointer;
>          typedef element_type &                  reference;
>          typedef const element_type &            const_reference;
> [...]
>
>
> My example block_ptr_test2.cpp doesn't work yet but at least I can go
> from here.  That's the real stress test I was looking for.

I have to admit MSVC 2015 got a clean STL...

block_ptr_test2.cpp doesn't crash but some assertions are wrong.

Is there any plans from Boost to make the Boost.Container work with 
inner smart pointers?  I don't think there is any other alternative if 
people want to plugin memory management.