/// Build from anything that has an indexmap and a storage compatible with this class
template <typename ISP> matrix_view(const ISP& X) : IMPL_TYPE(X.indexmap(), X.storage()) {}
/// Build from anything that has an indexmap and a storage compatible with this class
template<typename ISP> matrix_view(const ISP & X): impl_type(X.indexmap(),X.storage()) {}
/// Build from anything that has an indexmap and a storage compatible with this class
template<typename ISP> array_view(const ISP & X): BaseType(X.indexmap(),X.storage()) {}
/// Build from anything that has an indexmap and a storage compatible with this class
template <typename ISP> array_view(const ISP& X) : IMPL_TYPE(X.indexmap(), X.storage()) {
// to be activated
static_assert(IsConst || (!ISP::is_const), "Cannot construct a non const view from a const one !");
}