void copy(array<T, S>& out, const array<J, D>& in)
{
CHECK(out.length() == in.length(), erange);
loops::loop<loops::assign_copy_class<T&, const J&> >(
out.derived(), in.derived());
}
void swap(array<J, D>& a)
{
this->derived() = a.derived();
}