c ++模板结构“使用类型= struct_name”

Question

template <::size_t... Is>
struct int_pack {
  using type = int_pack;
};

1. why do we need using type = int_pack here ?
2. When we use a pattern like using type = struct_name , is there any specific usage ?

Answer 1

You don't need using type = int_pack , it's just a shorter way to write int_pack .

type is usually used in type_traits for meta programming. For example, std::enable_if defines a name type if it's template argument is true . There are more of these helper functions/structures that define a name type . It's just a name that has stuck, like using i in a for loop index.