initializer_list可以让我们像数组初始化列表一样初始化我们的类。

编译器遇到一个初始化列表时，首先会将其转换成为一个std::initializer_list. 所以在创建我们的类的时候，我们创建一个构造函数，该构造函数是以std::initializer_list作为参数，那么我们就可以使用初始化列表作为输入的参数。

std::initializer_list
header: 

  1. #include <cassert> // for assert()
  2. #include <initializer_list> // for std::initializer_list
  3. #include <iostream>
  5. class IntArray
  6. {
  7. private:
  8.     int m_length{};
  9.     int *m_data{};
  11. public:
  12.     IntArray() = default;
  14.     IntArray(int length) :
  15.         m_length{ length },
  16.         m_data{ new int[length]{} }
  17.     {
  19.     }
  21.     IntArray(std::initializer_list<int> list) : // allow IntArray to be initialized via list initialization
  22.         IntArray(static_cast<int>(list.size())) // use delegating constructor to set up initial array
  23.     {
  24.         // Now initialize our array from the list
  25.         int count{ 0 };
  26.         for (auto element : list)
  27.         {
  28.             m_data[count] = element;
  29.             ++count;
  30.         }
  31.     }
  33.     ~IntArray()
  34.     {
  35.         delete[] m_data;
  36.         // we don't need to set m_data to null or m_length to 0 here, since the object will be destroyed immediately after this function anyway
  37.     }
  39.     IntArray(const IntArray&) = delete; // to avoid shallow copies
  40.     IntArray& operator=(const IntArray& list) = delete; // to avoid shallow copies
  42.     int& operator[](int index)
  43.     {
  44.         assert(index >= 0 && index < m_length);
  45.         return m_data[index];
  46.     }
  48.     int getLength() const { return m_length; }
  49. };
  51. int main()
  52. {
  53.     IntArray array{ 5, 4, 3, 2, 1 }; // initializer list
  54.     for (int count{ 0 }; count < array.getLength(); ++count)
  55.         std::cout << array[count] << ' ';
  57.     return 0;
  58. }

Reference

https://www.learncpp.com/cpp-tutorial/stdinitializer_list/