自己手撸一个initializer_list()

//my_initializer_list.h
namespace std
{
  template <class T>
  class my_initializer_list
  {
  public:
    using value_type = T;
    using reference = const T&;
    using const_reference = const T&;
    using size_type = size_t;

    my_initializer_list() noexcept : __begin(nullptr), __size(0) {}
  
    my_initializer_list(const T* __b, size_t __s) noexcept : __begin(__b), __size(__s){}
    
    const T*  begin() const noexcept {return __begin;}
    const T* end() const noexcept {return __begin+ __size;}
    size_t size() const noexcept { return __size;}
  private:
    const T* __begin;
    size_t __size;
  };
}

int main()
{
    int array[] = {1,2,3};
    std::my_initializer_list<int> a = std::my_initializer_list<int>(array,sizeof(array)/sizeof(array[0]));

    for (const int& value : a) 
    {
        std::cout << value << " ";
    }
    return 0;
} 

使用

#include <iostream>
#include <my_initializer_list.h>

class MyArray
{
public:
  MyArray(std::my_initializer_list<int> values)
  {
    size_ = values.size();
    data_ = new int[size_];
    int i = 0;
    for(auto value : values)
    {
        data_[i++] = value;
    }
  }

  void print()
  {
    for (int i = 0; i < size_; ++i) {
        std::cout << data_[i] << " ";
    }
    std::cout << std::endl;
  }

private:
    int* data_;
    size_t size_;
};

int main()
{
    int array[] = {1,2,3,4};
    MyArray arr = MyArray(std::my_initializer_list<int>(array,sizeof(array)/sizeof(array[0])));

    //等价于
    MyArray arr = {1, 2, 3, 4};
    arr.print();
    return 0;
}