Class unchecked_reference

include/pybind11/numpy.h:646–730

 */
template <typename T, ssize_t Dims>
class unchecked_reference {
protected:
    static constexpr bool Dynamic = Dims < 0;
    const unsigned char *data_;
    // Storing the shape & strides in local variables (i.e. these arrays) allows the compiler to
    // make large performance gains on big, nested loops, but requires compile-time dimensions
    conditional_t<Dynamic, const ssize_t *, std::array<ssize_t, (size_t) Dims>> shape_, strides_;
    const ssize_t dims_;

    friend class pybind11::array;
    // Constructor for compile-time dimensions:
    template <bool Dyn = Dynamic>
    unchecked_reference(const void *data,
                        const ssize_t *shape,
                        const ssize_t *strides,
                        enable_if_t<!Dyn, ssize_t>)
        : data_{reinterpret_cast<const unsigned char *>(data)}, dims_{Dims} {
        for (size_t i = 0; i < (size_t) dims_; i++) {
            shape_[i] = shape[i];
            strides_[i] = strides[i];
        }
    }
    // Constructor for runtime dimensions:
    template <bool Dyn = Dynamic>
    unchecked_reference(const void *data,
                        const ssize_t *shape,
                        const ssize_t *strides,
                        enable_if_t<Dyn, ssize_t> dims)
        : data_{reinterpret_cast<const unsigned char *>(data)}, shape_{shape}, strides_{strides},
          dims_{dims} {}

public:
    /**
     * Unchecked const reference access to data at the given indices.  For a compile-time known
     * number of dimensions, this requires the correct number of arguments; for run-time
     * dimensionality, this is not checked (and so is up to the caller to use safely).
     */
    template <typename... Ix>
    const T &operator()(Ix... index) const {
        static_assert(ssize_t{sizeof...(Ix)} == Dims || Dynamic,
                      "Invalid number of indices for unchecked array reference");
        return *reinterpret_cast<const T *>(data_
                                            + byte_offset_unsafe(strides_, ssize_t(index)...));
    }
    /**
     * Unchecked const reference access to data; this operator only participates if the reference
     * is to a 1-dimensional array.  When present, this is exactly equivalent to `obj(index)`.
     */
    template <ssize_t D = Dims, typename = enable_if_t<D == 1 || Dynamic>>
    const T &operator[](ssize_t index) const {
        return operator()(index);
    }

    /// Pointer access to the data at the given indices.
    template <typename... Ix>
    const T *data(Ix... ix) const {
        return &operator()(ssize_t(ix)...);
    }