在包含多种类型的容器中传播 scoped_allocator_adaptor 的惯用方式

问题描述

使用包含异构类型的容器，例如struct S1 下面，我通过重新绑定作为构造函数一部分获得的上游分配器将分配器传播到成员元素[同样适用于将分配器作为参数的扩展复制和移动构造函数]。问题是这是否是传播分配器的惯用方式，还是除了显式调用 allocator_traits 之外还有其他方式？

#include <iostream>
#include <cassert>
#include <vector>
#include <scoped_allocator>

// Move allocator and container aliases into namepsace 
namespace custom
{
    template <typename T>
    struct MyAlloc
    {
        using value_type = T;
        MyAlloc(const std::string &scope) noexcept : _scope(scope)  {} 

        // Rebinding allocatos to different type 
        template <class U> 
        MyAlloc(const MyAlloc<U> & other) noexcept : _scope(other._scope)  {}

        // Allow for move operations to be noexcept
        //using is_always_equal = std::true_type;

        value_type*  allocate(std::size_t n) noexcept
        {
            std::cout << "Allocating " << n << " objects within " << _scope << " from " << __PRETTY_FUNCTION__ << std::endl;
            return static_cast<value_type*>(::operator new (n*sizeof(value_type)));
        }
        void deallocate(value_type* p,std::size_t n) noexcept
        {
            std::cout << "Deallocating " << n << " objects within " << _scope << " from " << __PRETTY_FUNCTION__ << std::endl;
            ::operator delete(p);
        }
        std::string _scope;
    };

    // Allocators compare equal to enable one allocator to de-allocate memory
    // from another
    template <typename T>
    bool operator==(const MyAlloc<T> &x1,const MyAlloc<T> &x2) noexcept
    {
        return true;
    }

    template <typename T>
    bool operator!=(const MyAlloc<T> &x1,const MyAlloc<T> &x2) noexcept
    {
        return !(x1 == x2);
    }

    template <typename T>
    using allocator = std::scoped_allocator_adaptor<MyAlloc<T>>;

    template <typename T> //  adaptor to propagate
    using vector = std::vector<T,allocator<T>>;

    template <typename T> 
    using bstr = std::basic_string<T,std::char_traits<T>,allocator<T>>;
    using string = bstr<char>;
}

struct S1
{
   using allocator_type = custom::allocator<std::byte>;
   S1(const allocator_type &alloc) : str("This is a very long string indeed..",std::allocator_traits<allocator_type>::rebind_alloc<char>(alloc)),vec(std::allocator_traits<allocator_type>::rebind_alloc<float>(alloc)) 
   {
      vec.emplace_back();
      std::cout << __PRETTY_FUNCTION__ << std::endl;
   }
   S1(const S1 &other,const allocator_type &alloc)  : str(other.str,vec(std::allocator_traits<allocator_type>::rebind_alloc<float>(alloc)) 
   {
      std::cout << __PRETTY_FUNCTION__ << std::endl;
   }
   custom::string str;
   custom::vector<float> vec;
};



int main()
{
   custom::allocator<std::byte> sc{"scope1"};
   custom::vector<S1> cv(sc);
   cv.emplace_back();
}

解决方法

暂无找到可以解决该程序问题的有效方法，小编努力寻找整理中！

如果你已经找到好的解决方法，欢迎将解决方案带上本链接一起发送给小编。

小编邮箱:dio#foxmail.com (将#修改为@）