Refactor Backend and Layer interfaces

include/tensor.hpp

@@ -0,0 +1,47 @@
+#pragma once
+
+#include <cstddef>
+#include <vector>
+
+#include "backend.hpp"
+#include "shape.hpp"
+
+namespace CUDANet
+{
+
+enum class DType
+{
+    FLOAT32,
+    // FLOAT16,  // Not implemented yet
+    // INT32,  // Not implemented yet
+};
+
+class Tensor
+{
+public:
+
+    Tensor() = default;
+    Tensor(Shape shape, DType dtype, CUDANet::Backend::IBackend* backend);
+    ~Tensor();
+
+    size_t size() const;
+    size_t numel() const;
+
+    template <typename T>
+    const T* data() const;
+
+    template <typename T>
+    T* data();
+
+private:
+    Shape       shape;
+    DType       dtype;
+
+    size_t total_elms;
+    size_t total_size;
+
+    CUDANet::Backend::IBackend*   backend;
+    void*       d_ptr;
+};
+
+} // namespace CUDANet