Re: [boost] Request for help in porting colony to boost from experienced container boost dev

Subject: Re: [boost] Request for help in porting colony to boost from experienced container boost dev
From: Soul Studios (matt_at_[hidden])
Date: 2015-08-25 06:07:51

> Matt,
>
> Regarding your use of allocators in your implementation:
> a. Support the C++ allocator model
>    1. Either use a.allocate(size) or allocator_traits<A>::allocate(a,
> size, hint) if you want to supply a hint, but don't bother calling
> a.allocate(size, 0) - you alienate anyone who writes a C++11 allocator
> that may not provide an allocate(size, hint) member.

Right - this might be something that has to change for the boost 
submission, the original is designed to work with both C++0x and C++11, 
and the hints made a substantial difference to speed with std::allocator.

>    2. Use allocator_traits<A>::construct(a, ...) and
> allocator_traits<A>::destroy(a) instead of a.construct(...) and
> a.destroy(...)

Why, and is there a C++0x-friendly way of doing the same thing?

>    3. Use allocator_traits<A> to obtain the type members (pointer, rebind, etc.)
> (You could use boost::allocator_traits if you want to support pre-C++11)

What is the advantage of doing this?

> b. Use a compressed_pair<> or the EBCO to reduce the storage for when
> stateless allocators are supplied (i.e. instead of the 1 + 1 bytes
> that would be used for the empty objects).

Empty base optimization is not something I understand at this point. 
I've read a bit about it but I am not sure in which particular area of 
the colony it would make a difference in?

> c. Support element_type's whose constructor might throw: Do you catch,
> accordingly destroy any constructed elements, deallocate any allocated
> elements, before rethrowing?

I guess that makes sense in the limited scenario where memory is full.

My general feeling is more in line with Mike Acton's in that if 
something throws, you've got a problem anyway - peaceably unrolling 
isn't really helping anyone.

But I grant that in the context of boost, and in some scenarios, this is 
vital, and will look at adding it.

Thank you,
Matt