Re: [boost] [container] varray aka static_vector

Subject: Re: [boost] [container] varray aka static_vector
From: Nevin Liber (nevin_at_[hidden])
Date: 2013-02-12 18:16:37

On 12 February 2013 14:02, Krzysztof Czainski <1czajnik_at_[hidden]> wrote:

> 2013/2/12 Nevin Liber <nevin_at_[hidden]>
>
>
> I am not familiar with C++11 initialization syntax details, I only read
> about that, and I'm stuck with C++03 for now. Are you suggesting, that this
> would mean adding a lot of (too many?) member functions?
>

There are some corner cases where list initialization behaves differently
than direct initialization.

Take the following example:

template<typename T>
struct ListInitializationAllocator
{
    typedef T value_type;
    typedef typename std::aligned_storage<sizeof(T), alignof(T)>::type
storage_type;

    T* allocate(size_t n) { return static_cast<T*>(static_cast<void*>(::new
storage_type[n])); }
    void deallocate(T* p, size_t) { ::delete []
static_cast<storage_type*>(static_cast<void*>(p)); }

    template<typename... Args>
    void construct(T* c, Args&&... args)
    { ::new (static_cast<void*>(c)) T{ std::forward<Args>(args)... }; }
};

    vector<vector<int>> vd;
    vd.emplace_back(2);
    assert(2 == vd.back().size());

    vector<vector<int>, ListInitializationAllocator<vector<int>>> vl;
    vl.emplace_back(2);
    assert(1 == vl.back().size());

The element in vd is a vector<int> of 2 elements which are
value-initialized to 0.
The element in vl is a vector<int> of 1 element copy-initialized to 2.

>
> Anyway, personally I'm only interested in features, that can be added for
> C++03 ;-)

Boost needs to be more concerned than that.

> And noinit_push*/noinit_resize (enabled_if< is_pod<value_type> >)
> are things I have use cases for.
>

That is the difference between designing a library for yourself and a
library for the community at large.

This use case might not be important enough to implement, but it should at
least be considered.
-- 
 Nevin ":-)" Liber  <mailto:nevin_at_[hidden]>  [phone]