Re: [boost] static_vector using aligned_storage

Subject: Re: [boost] static_vector using aligned_storage
From: Nevin Liber (nevin_at_[hidden])
Date: 2012-12-12 17:57:04

On 12 December 2012 15:39, Adam Wulkiewicz <adam.wulkiewicz_at_[hidden]>wrote:

> Personally I'd like to have exception thrown only in at(). Only this
> method throws out_of_range exception in std::vector and boost::array. So
> operator[], pop_back(), erase() shouldn't throw IMO. The problem is with
> vector's methods which may throw bad_alloc exception, like push_back() or
> insert(). I think that in general we shouldn't provide mechanisms (throw
> exceptions) which majority of users wouldn't need. So I see a few possible
> solutions:
> 1. Leave static_vector as it is now, throwing exceptions.
> 2. Make error handling dependent on some macro e.g.
> BOOST_STATIC_VECTOR_USE_**EXCEPTIONS
> 3. Use slightly different class interface and take additional template
> parameter: static_vector<T, N, ErrHandling = use_asserts>
> 4. Use asserts in static_vector and provide a wrapper throwing exceptions.
> Or if people are concerned about the efficiency, implement a base class and
> derive both implementations from it.
>

Another possible solution is to fall back on an allocator if there isn't
enough room in the embedded storage.  The signature would be something like

static_vector<T, N, A = std::allocator<T>>

And you could provide null_allocator_assert and null_allocator_throw as
options (or make one of those the default), as it is now the responsibility
of the allocator, not static_vector, to throw or not throw.

I don't know if methods returning pointers to internal elements (data() and
> c_array()) are necessary in resizable container, especially if those are
> really aligned_storages.

data() certainly is.  Again, I believe the interface should be as close to
a superset of C++11 std::vector as possible.  I know I'd like to use it as
a drop-in replacement for std::vector.  Every arbitrary difference makes it
a less useful class.
-- 
 Nevin ":-)" Liber  <mailto:nevin_at_[hidden]>  [phone]