refactor(expression): delete the move assignment operator

include/boost/numeric/ublas/tensor/expression.hpp

@@ -128,6 +128,7 @@ struct tensor_expression
     /// @brief The copy constructor is deleted to avoid expensive copies or sometimes object slicing.
     tensor_expression(const tensor_expression&) = delete;
     tensor_expression& operator=(const tensor_expression&) = delete;
+    constexpr tensor_expression& operator=(tensor_expression&&) noexcept = delete;
 
 /**
  * @brief This is the only way to discourage the users from using `std::move` on the local 
@@ -142,7 +143,6 @@ struct tensor_expression
  */
 protected :
     constexpr tensor_expression(tensor_expression&&) noexcept = default;
-    constexpr tensor_expression& operator=(tensor_expression&&) noexcept = default;
     explicit tensor_expression() = default;
 
     /// @brief This the only way to access the protected move constructor of other expressions.
@@ -176,6 +176,7 @@ struct binary_tensor_expression
     /// @brief The copy constructor is deleted to avoid expensive copies or sometimes object slicing.
     binary_tensor_expression(const binary_tensor_expression& l) = delete;
     binary_tensor_expression& operator=(binary_tensor_expression const& l) noexcept = delete;
+    constexpr binary_tensor_expression& operator=(binary_tensor_expression&& l) noexcept = delete;
 
     [[nodiscard]] constexpr auto const& left_expr() const noexcept{ return cast_tensor_expression(el); }
     [[nodiscard]] constexpr auto const& right_expr() const noexcept{ return cast_tensor_expression(er); }
@@ -196,7 +197,6 @@ struct binary_tensor_expression
  */
 protected:
     constexpr binary_tensor_expression(binary_tensor_expression&& l) noexcept = default;
-    constexpr binary_tensor_expression& operator=(binary_tensor_expression&& l) noexcept = default;
 
     /// @brief This the only way to access the protected move constructor of other expressions.
     template<class, class, class> friend struct unary_tensor_expression;
@@ -250,6 +250,7 @@ struct unary_tensor_expression
     /// @brief The copy constructor is deleted to avoid expensive copies or sometimes object slicing.
     unary_tensor_expression(unary_tensor_expression const& l) = delete;
     unary_tensor_expression& operator=(unary_tensor_expression const& l) noexcept = delete;
+    constexpr unary_tensor_expression& operator=(unary_tensor_expression&& l) noexcept = delete;
 
     [[nodiscard]] constexpr auto const& expr() const noexcept{ return cast_tensor_expression(e); }
 
@@ -269,7 +270,6 @@ struct unary_tensor_expression
  */
 protected:
     constexpr unary_tensor_expression(unary_tensor_expression&& l) noexcept = default;
-    constexpr unary_tensor_expression& operator=(unary_tensor_expression&& l) noexcept = default;
 
     /// @brief This the only way to access the protected move constructor of other expressions.
     template<class, class, class> friend struct unary_tensor_expression;