From cffee479d3e09c5507db24f1467beb858f08f1dc Mon Sep 17 00:00:00 2001
From: Sam Hocevar <sam@hocevar.net>
Date: Thu, 25 Jun 2020 13:01:37 +0200
Subject: [PATCH] Add narray_view class, similar to std::span for n-dimensional
 arrays.

---
 include/lol/private/base/narray.h | 159 ++++++++++++++++++++----------
 1 file changed, 106 insertions(+), 53 deletions(-)

diff --git a/include/lol/private/base/narray.h b/include/lol/private/base/narray.h
index 7f45b923..eebe06d6 100644
--- a/include/lol/private/base/narray.h
+++ b/include/lol/private/base/narray.h
@@ -15,127 +15,180 @@
 //
 // The narray class
 // ————————————————
-// An N-dimensional row-major array template class
+// An n-dimensional row-major array template class
 //
 
 #include <lol/vector>  // lol::vec_t
 #include <vector>      // std::vector
+#include <utility>     // std::index_sequence
 
 namespace lol
 {
 
-template<typename T, size_t N>
-class [[nodiscard]] narray
+template<typename T, size_t N, typename container_type>
+class [[nodiscard]] narray_base
 {
 public:
-    typedef T value_type;
-
-    inline narray() = default;
-    inline ~narray() = default;
-
-    // Construct array with args: size1, size2, ..., sizen
-    template<typename... I> inline narray(I... sizes)
-    {
-        static_assert(N == sizeof...(I));
-        resize(sizes...);
-    }
+    using value_type = T;
 
-    // Construct array with integer vec_t arg:
-    inline narray(vec_t<int, N> const &sizes)
+    // Return sizes of each dimension
+    inline vec_t<int, N> sizes() const
     {
-        resize(sizes);
+        return vec_t<int, N>(m_sizes);
     }
 
-    // Empty array
-    inline void clear() { resize(vec_t<size_t, N>(0)); }
+    // Size in number of elements and in bytes
+    inline size_t size() const { return size_helper(std::make_index_sequence<N>{}); }
+    inline size_t bytes() const { return size() * sizeof(value_type); }
 
-    // Access element i
+    // Access element i in row-major fashion
     inline value_type &operator[](size_t i)
     {
-        return m_data[i];
+        return data()[i];
     }
 
     inline value_type const &operator[](size_t i) const
     {
-        return m_data[i];
+        return data()[i];
     }
 
-    // Access element (i, j, .., z) in row-major fashion
+    // Access element (i, j, .., z)
     template<typename... I>
     inline value_type &operator()(I... indices)
     {
         static_assert(N == sizeof...(I));
-        return m_data[offset(indices...)];
+        return data()[offset(indices...)];
     }
 
     template<typename... I>
     inline value_type const &operator()(I... indices) const
     {
         static_assert(N == sizeof...(I));
-        return m_data[offset(indices...)];
+        return data()[offset(indices...)];
     }
 
     inline value_type &operator()(vec_t<int, N> const &indices)
     {
-        return m_data[offset_helper(indices, std::make_index_sequence<N>{})];
+        return data()[offset_helper(indices, std::make_index_sequence<N>{})];
     }
 
     inline value_type const &operator()(vec_t<int, N> const &indices) const
     {
-        return m_data[offset_helper(indices, std::make_index_sequence<N>{})];
+        return data()[offset_helper(indices, std::make_index_sequence<N>{})];
     }
 
-    // Resize array with a list of sizes (size1, size2, ..., sizen)
-    template<typename... I>
-    inline void resize(I... sizes)
+protected:
+    template <size_t... I>
+    inline size_t size_helper(std::index_sequence<I...>) const
     {
-        static_assert(N == sizeof...(I));
-        m_data.resize((size_t(sizes) * ... * 1));
-        m_sizes = { size_t(sizes)... };
+        return (size_t(m_sizes[I]) * ... * 1);
     }
 
-    inline void resize(vec_t<int, N> const &sizes)
+    template<typename... I>
+    inline size_t offset(size_t i, I... indices) const
     {
-        resize_helper(sizes, std::make_index_sequence<N>{});
+        if constexpr(sizeof...(I) > 0)
+            i += m_sizes[N - sizeof...(I) - 1] * offset(indices...);
+        return i;
     }
 
-    // Return sizes of each dimension
-    inline vec_t<int, N> sizes() const
+    template <size_t... I>
+    inline size_t offset_helper(vec_t<int, N> const &sizes, std::index_sequence<I...>) const
     {
-        return vec_t<int, N>(this->m_sizes);
+        return offset(size_t(sizes[I])...);
     }
 
-    inline value_type *data() { return m_data.data(); }
-    inline value_type const *data() const { return m_data.data(); }
-    inline size_t size() const { return m_data.size(); }
-    inline size_t bytes() const { return size() * sizeof(value_type); }
+    vec_t<size_t, N> m_sizes { 0 };
 
 private:
-    template<typename... I> size_t offset(size_t i, I... indices) const
+    // Use CRTP to access data() from the child class
+    inline value_type *data()
     {
-        if constexpr(sizeof...(I) > 0)
-            i += m_sizes[N - sizeof...(I) - 1] * offset(indices...);
-        return i;
+        return static_cast<container_type *>(this)->data();
     }
 
-    template <std::size_t... I>
-    size_t offset_helper(vec_t<int, N> const &sizes, std::index_sequence<I...>) const
+    inline value_type const *data() const
     {
-        return offset(size_t(sizes[I])...);
+        return static_cast<container_type const *>(this)->data();
     }
+};
+
+
+template<typename T, size_t N>
+class [[nodiscard]] narray : public narray_base<T, N, narray<T, N>>
+{
+public:
+    using value_type = T;
 
-    template <std::size_t... I>
-    void resize_helper(vec_t<int, N> const &sizes, std::index_sequence<I...>)
+    inline narray() = default;
+    inline ~narray() = default;
+
+    // Construct array with args: size1, size2, ..., sizen
+    template<typename... I> inline narray(I... sizes)
     {
-        resize(sizes[I]...);
+        static_assert(N == sizeof...(I));
+        resize(sizes...);
     }
 
-    vec_t<size_t, N> m_sizes { 0 };
+    // Construct array with integer vec_t arg:
+    inline narray(vec_t<int, N> const &sizes)
+    {
+        resize(sizes);
+    }
+
+    // Empty array
+    inline void clear() { resize(vec_t<size_t, N>(0)); }
+
+    // Resize array with a list of sizes (size1, size2, ..., sizen)
+    template<typename... I>
+    inline void resize(I... sizes)
+    {
+        static_assert(N == sizeof...(I));
+        this->m_sizes = { size_t(sizes)... };
+        m_data.resize(this->size());
+    }
+
+    template<typename U>
+    inline void resize(vec_t<U, N> const &sizes)
+    {
+        this->m_sizes = vec_t<size_t, N>(sizes);
+        m_data.resize(this->size());
+    }
+
+    // Access data directly
+    inline value_type *data() { return m_data.data(); }
+    inline value_type const *data() const { return m_data.data(); }
+
+private:
     std::vector<T> m_data;
 };
 
 template<typename T> using array2d = narray<T, 2>;
 template<typename T> using array3d = narray<T, 3>;
 
+template<typename T, size_t N>
+class [[nodiscard]] narray_view : public narray_base<T, N, narray_view<T, N>>
+{
+public:
+    using value_type = T;
+
+    template<typename U>
+    inline narray_view(narray_base<T, N, U> &other)
+      : m_data(&other[0])
+    {
+        this->m_sizes = vec_t<size_t, N>(other.sizes());
+    }
+
+    // Access data directly
+    inline value_type *data() { return m_data; }
+    inline value_type const *data() const { return m_data; }
+
+private:
+    T *m_data;
+};
+
+template<typename T> using array2d_view = narray_view<T, 2>;
+template<typename T> using array3d_view = narray_view<T, 3>;
+
 } // namespace lol