标准模板库中容器对初始化列表的支持源自<initializer_list>这个头文件中initialize_list类模板的支持。程序员只要#include了<initializer_list>头文件，并且声明一个以initialize_list<T>模板类为参数的构造函数，同样可以使得自定义的类使用列表初始化。

在C++11中，列表初始化是唯一一种可以防止类型收窄的初始化方式。

列表初始化改变了C++中对类型初始化的一些基本模式，将标准程序库跟语言拉得更近了。这样的做法有效地统一了内置类型和自定义类型的行为。这也是C++11设计所遵循的一个思想，即通用为本，专用为末。

std::initializer_list

initializer_list objects are automatically constructed as if an array of elements of type T was allocated, with each of the elements in the list being copy-initialized to its corresponding element in the array, using any necessary non-narrowing implicit conversions.

  /// initializer_list
  template<class _E>
    class initializer_list
    {
    public:
      typedef _E        value_type;
      typedef const _E&     reference;
      typedef const _E&     const_reference;
      typedef size_t        size_type;
      typedef const _E*     iterator;
      typedef const _E*     const_iterator;

    private:
      iterator          _M_array;
      size_type         _M_len;

      // The compiler can call a private constructor.
      constexpr initializer_list(const_iterator __a, size_type __l)
      : _M_array(__a), _M_len(__l) { }

    public:
      constexpr initializer_list() noexcept
      : _M_array(0), _M_len(0) { }

      // Number of elements.
      constexpr size_type
      size() const noexcept { return _M_len; }

      // First element.
      constexpr const_iterator
      begin() const noexcept { return _M_array; }

      // One past the last element.
      constexpr const_iterator
      end() const noexcept { return begin() + size(); }
    };

  /**
   *  @brief  Return an iterator pointing to the first element of
   *          the initializer_list.
   *  @param  __ils  Initializer list.
   */
  template<class _Tp>
    constexpr const _Tp*
    begin(initializer_list<_Tp> __ils) noexcept
    { return __ils.begin(); }

  /**
   *  @brief  Return an iterator pointing to one past the last element
   *          of the initializer_list.
   *  @param  __ils  Initializer list.
   */
  template<class _Tp>
    constexpr const _Tp*
    end(initializer_list<_Tp> __ils) noexcept
    { return __ils.end(); }
}

使用initializer_list的实例

/**
   *  @brief  Set value to string constructed from initializer %list.
   *  @param  __l  std::initializer_list.
   */
  basic_string&
  operator=(initializer_list<_CharT> __l)
  {
    this->assign(__l.begin(), __l.size());
    return *this;
  }

参考：
stl源码
《深入理解C++11：C++11新特性解析与应用》