I came across an interesting quiz question at here:
Write a translation unit containing a class type T, such that
std::is_empty_v<T>is true, and yetsizeof(T)is greater than 1.
I'v thought about it for some time, but no solution.
How to make a type T that std::is_empty_v<T> && sizeof(T) > 1 is true?
std::is_empty checks if there are no members. You can use alignment to force a size greater than 1:
struct alignas(2) T {};
static_assert(std::is_empty_v<T>);
static_assert(sizeof(T) > 1);
Since two identical empty classes cannot share the same address, we can create a class that inherits an empty base and also has an empty base as a member to prohibit EBO and make its size greater than 1.
#include<type_traits>
struct B { };
struct D : B { [[no_unique_address]] B b; };
static_assert(std::is_empty_v<D> && sizeof(D) > 1);