Changes to NullPtrTable, NullPtrVector to remove unneeded methods.

Also added const qualifier to enable deployment of NullPtrTable
to work.

Author: oleksandr-pavlyk

dpctl/tensor/libtensor/include/utils/type_dispatch.hpp

@@ -337,87 +337,32 @@ template <typename T> struct GetTypeid
 template <typename FunPtrT> struct NullPtrVector
 {
 
-    using iterator_category = std::forward_iterator_tag;
-    using different_type = std::ptrdiff_t;
     using value_type = FunPtrT;
-    using pointer = value_type *;
-    using reference = value_type &;
+    using const_reference = value_type const &;
 
     NullPtrVector() : val(nullptr) {}
 
-    reference operator*()
+    const_reference operator[](int) const
     {
         return val;
     }
 
-    reference operator[](int)
-    {
-        return val;
-    }
-
-    NullPtrVector<FunPtrT> &operator++()
-    {
-        return *this;
-    }
-    NullPtrVector<FunPtrT> operator++(int)
-    {
-        return *this;
-    }
-
-    friend bool operator==(const NullPtrVector<FunPtrT> &a,
-                           const NullPtrVector<FunPtrT> &b)
-    {
-        return true;
-    }
-    friend bool operator!=(const NullPtrVector<FunPtrT> &a,
-                           const NullPtrVector<FunPtrT> &b)
-    {
-        return false;
-    }
-
 private:
     value_type val;
 };
 
 /*! @brief Class to generate table of null function pointers */
 template <typename FunPtrT> struct NullPtrTable
 {
-    using iterator_category = std::forward_iterator_tag;
-    using different_type = std::ptrdiff_t;
     using value_type = NullPtrVector<FunPtrT>;
-    using pointer = value_type *;
-    using reference = value_type &;
+    using const_reference = value_type const &;
 
     NullPtrTable() : val() {}
 
-    reference operator*()
+    const_reference operator[](int) const
     {
         return val;
     }
-    reference operator[](int)
-    {
-        return val;
-    }
-
-    NullPtrTable<FunPtrT> &operator++()
-    {
-        return *this;
-    }
-    NullPtrTable<FunPtrT> operator++(int)
-    {
-        return *this;
-    }
-
-    friend bool operator==(const NullPtrTable<FunPtrT> &a,
-                           const NullPtrTable<FunPtrT> &b)
-    {
-        return true;
-    }
-    friend bool operator!=(const NullPtrTable<FunPtrT> &a,
-                           const NullPtrTable<FunPtrT> &b)
-    {
-        return false;
-    }
 
 private:
     value_type val;