#include <string>
#include <cassert>
+
+template <class ...>
+struct never {
+ enum { value = 0 };
+};
+
+struct NoValueCtor
+{
+ NoValueCtor() : id(++count) {}
+ NoValueCtor(NoValueCtor const & other) : id(other.id) { ++count; }
+
+ // The constexpr is required to make is_constructible instantiate this template.
+ // The explicit is needed to test-around a similar bug with is_convertible.
+ template <class T>
+ constexpr explicit NoValueCtor(T)
+ { static_assert(never<T>::value, "This should not be instantiated"); }
+
+ static int count;
+ int id;
+};
+
+int NoValueCtor::count = 0;
+
+
+struct NoValueCtorEmpty
+{
+ NoValueCtorEmpty() {}
+ NoValueCtorEmpty(NoValueCtorEmpty const &) {}
+
+ template <class T>
+ constexpr explicit NoValueCtorEmpty(T)
+ { static_assert(never<T>::value, "This should not be instantiated"); }
+};
+
int main()
{
{
assert(std::get<1>(t) == nullptr);
assert(std::get<2>(t) == "text");
}
+ // __tuple_leaf<T> uses is_constructible<T, U> to disable its explicit converting
+ // constructor overload __tuple_leaf(U &&). Evaluating is_constructible can cause a compile error.
+ // This overload is evaluated when __tuple_leafs copy or move ctor is called.
+ // This checks that is_constructible is not evaluated when U == __tuple_leaf.
+ {
+ std::tuple<int, NoValueCtor, int, int> t(1, NoValueCtor(), 2, 3);
+ assert(std::get<0>(t) == 1);
+ assert(std::get<1>(t).id == 1);
+ assert(std::get<2>(t) == 2);
+ assert(std::get<3>(t) == 3);
+ }
+ {
+ std::tuple<int, NoValueCtorEmpty, int, int> t(1, NoValueCtorEmpty(), 2, 3);
+ assert(std::get<0>(t) == 1);
+ assert(std::get<2>(t) == 2);
+ assert(std::get<3>(t) == 3);
+ }
// extensions
{
std::tuple<int, char*, std::string> t(2);