Create the simplest dispenser with two template arguments

Question

I am extremely new to C ++ memory management, but I want my hands dirty to build a simple allocator that would preallocate memory for some container.

I looked at the library of Alexandrescu Loki and tried to read some blogs, but it was all just for me to understand. I want to start from some primitive and working starting point, expand it and see how it develops. This is what I have now and what I understand (starting point):

template <class T>
struct Allocator {

    Allocator(){};

    template <class U>
    Allocator(Allocator<U> const&);

    T* allocate(size_t s) {
        return static_cast<T*>(::operator new(s * sizeof(T)));
    }

    void deallocate(T* p, size_t s) {
        ::operator delete(p);
    }

    void construct(T* p, T const& val) {
        ::new((void *)p) T(val);
    }

    void destroy(T* p) {
        return ((T *) p)->~T();
    }

    using value_type = T;

};

So now I can use it like this:

std::vector<int, Allocator<int> > vec;

This dispenser is very simple, and I understand what it does. Now I want to expand it a bit so that my client code looks like this:

std::vector<int, Allocator<int, 8> > vec;

, 8 . :

template <class T, size_t T_num_els>
struct Allocator {

    template <class U, size_t U_num_els>
    Allocator(Allocator<U, U_num_els> const&);

    ... I keep all the rest without changes just for testing reason

, , , rebind_alloc "type". , . , ?

Answer 1

, , , . allocator_traits adapter, , .

, std::list<int>, int, internal_node<int>. Allocator<int> Allocator<internal_node<int>>.

T, allocator_traits Alloc::rebind<T>::other (++ 98) , Alloc<T, Args...>, Alloc<U, Args...>.

, Allocator. , 8 , Args.

, ,

template<class U>
struct rebind
{
   using other = Allocator<U, T_num_els>;
};