/// @brief Data type of expression elements.

typedef typename ExpressionTraits<Derived>::Element Element;

/// @brief Number of dimensions (boost::mpl::int_).

typedef typename ExpressionTraits<Derived>::ND ND;

/// @brief Nested expression or element iterator.

typedef typename ExpressionTraits<Derived>::Iterator Iterator;

/// @brief Nested expression or element reference.

typedef typename ExpressionTraits<Derived>::Reference Reference;

/// @brief Nested expression or element value type.

typedef typename ExpressionTraits<Derived>::Value Value;

/// @brief Vector type for N-dimensional indices.

typedef Vector<Size,ND::value> Index;

/// @brief CRTP derived type.

typedef Derived Self;

/// @brief Return a single nested expression or element.

Reference operator[](Size n) const { return getSelf().operator[](n); }

/// @brief Return the first nested expression or element.

Reference front() const { return this->operator[](0); }

/// @brief Return the last nested expression or element.

Reference back() const { return this->operator[](this->template getSize<0>()-1); }

/// @brief Return an Iterator to the beginning of the expression.

Iterator begin() const { return getSelf().begin(); }

/// @brief Return an Iterator to one past the end of the expression.

Iterator end() const { return getSelf().end(); }

/// @brief Return the size of a specific dimension.

template <int P> Size getSize() const { return getSelf().template getSize<P>(); }

/// @brief Return a Vector of the sizes of all dimensions.

Index getShape() const { return getSelf().getShape(); }

/// @brief Return the total number of elements in the expression.

Size getNumElements() const { return getSelf().getNumElements(); }

/* ------------------------- STL Compatibility -------------------------- */

typedef Value value_type;

typedef Iterator iterator;

typedef Iterator const_iterator;

typedef Reference reference;

typedef Reference const_reference;

typedef Iterator pointer;

typedef Offset difference_type;

typedef Size size_type;

/// @brief Return the size of the first dimension.

size_type size() const { return this->template getSize<0>(); }

/// @brief Return true if the first dimension has no elements.

bool empty() const { return this->template getSize<0>() == 0; }

/* ---------------------------------------------------------------------- */

Self & getSelf() { return *static_cast<Self *>(this); }

Self const & getSelf() const { return *static_cast<Self const *>(this); }