I'm using a "fixed type compile-time list" for a project of mine. Recently I tested this project for compatibility with different compilers and I noticed the clang (3.8) can't compile my implementation.
This error appeared:
error: expected expression return
List<T, sizeof...(Ints1) + sizeof...(Ints2)>(this->get()..., rhs.get()...); >
The following part is extracted from my implementation of the compile time list:
template<class T, size_t TNum>
class List;
template<class T, size_t TNum>
class List: public List<T, TNum - 1>
{
protected:
T data;
template<size_t ... Ints1, size_t ... Ints2>
constexpr List<T, sizeof...(Ints1) + sizeof...(Ints2)> _concat(const List<T, sizeof...(Ints2)> rhs, std::index_sequence<Ints1...>, std::index_sequence<Ints2...>) const
{
return List<T, sizeof...(Ints1) + sizeof...(Ints2)>(this->get<Ints1>()..., rhs.get<Ints2>()...);
}
template<class ... TArgs>
constexpr List(T d, TArgs&& ... arg)
: List<T, TNum - 1>(std::forward<TArgs>(arg)...), data(d)
{
static_assert(TNum != sizeof...(TArgs), "Number of arguments and list size does not match!");
}
template<size_t TNum2, typename Indices1 = std::make_index_sequence<TNum>, typename Indices2 = std::make_index_sequence<TNum2>>
constexpr List<T, TNum + TNum2> concat(const List<T, TNum2>& rhs) const
{
return this->_concat(rhs, Indices1(), Indices2());
}
template<size_t TI>
constexpr T get() const
{
static_assert(TI < TNum, "Element out of valid range!");
static_assert(TI >= 0, "Element out of valid range!");
return static_cast<List<T, TNum - TI> >(*this).get();
}
};
Additional there are two spezialisation for TNum=1 and TNum=0 that are missing in this example. I can add them if needed
I hope you can help my find the error that creates this problem
Edit: Thanks Jarod42 for the answer. With his help i found this: Where and why do I have to put the "template" and "typename" keywords? That exlains things further.