fix(expression): disable the move constructor for public use to avoid…

… undefined behaviour

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

@@ -130,18 +130,18 @@ struct tensor_expression
     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 
- * expression because it works differently from the standard way to move the objects. This weird 
- * behaviour is due to `const reference`, which is impossible to move without constructing a new object. 
- * If the variable goes out of the scope, stored as a `const reference` inside the expression, 
- * it will be destroyed that will result in a dangling pointer. But this behaviour is helpful 
- * for the construction of an expression because the expression might contain a `const reference` 
- * object that will be passed around as a `const reference` rather than a copy, and we do not need to 
- * construct a whole new chunky object because, under the hood, we are just passing pointers around.
- * 
- */
 protected :
+    /**
+     * @brief This is the only way to discourage the users from using `std::move` on the local 
+     * expression because it works differently from the standard way to move the objects. This weird 
+     * behaviour is due to `const reference`, which is impossible to move without constructing a new object. 
+     * If the variable goes out of the scope, stored as a `const reference` inside the expression, 
+     * it will be destroyed that will result in a dangling pointer. But this behaviour is helpful 
+     * for the construction of an expression because the expression might contain a `const reference` 
+     * object that will be passed around as a `const reference` rather than a copy, and we do not need to 
+     * construct a whole new chunky object because, under the hood, we are just passing pointers around.
+     * 
+     */
     constexpr tensor_expression(tensor_expression&&) noexcept = default;
     explicit tensor_expression() = default;
 
@@ -184,18 +184,18 @@ struct binary_tensor_expression
     [[nodiscard]] inline 
     constexpr decltype(auto) operator()(size_type i) const { return op(left_expr()(i), right_expr()(i)); }
 
-/**
- * @brief This is the only way to discourage the users from using `std::move` on the local 
- * expression because it works differently from the standard way to move the objects. This weird 
- * behaviour is due to `const reference`, which is impossible to move without constructing a new object. 
- * If the variable goes out of the scope, stored as a `const reference` inside the expression, 
- * it will be destroyed that will result in a dangling pointer. But this behaviour is helpful 
- * for the construction of an expression because the expression might contain a `const reference` 
- * object that will be passed around as a `const reference` rather than a copy, and we do not need to 
- * construct a whole new chunky object because, under the hood, we are just passing pointers around.
- * 
- */
 protected:
+    /**
+     * @brief This is the only way to discourage the users from using `std::move` on the local 
+     * expression because it works differently from the standard way to move the objects. This weird 
+     * behaviour is due to `const reference`, which is impossible to move without constructing a new object. 
+     * If the variable goes out of the scope, stored as a `const reference` inside the expression, 
+     * it will be destroyed that will result in a dangling pointer. But this behaviour is helpful 
+     * for the construction of an expression because the expression might contain a `const reference` 
+     * object that will be passed around as a `const reference` rather than a copy, and we do not need to 
+     * construct a whole new chunky object because, under the hood, we are just passing pointers around.
+     * 
+     */
     constexpr binary_tensor_expression(binary_tensor_expression&& l) noexcept = default;
 
     /// @brief This the only way to access the protected move constructor of other expressions.
@@ -257,18 +257,18 @@ struct unary_tensor_expression
     [[nodiscard]] inline constexpr
     decltype(auto) operator()(size_type i) const { return op(expr()(i)); }
 
-/**
- * @brief This is the only way to discourage the users from using `std::move` on the local 
- * expression because it works differently from the standard way to move the objects. This weird 
- * behaviour is due to `const reference`, which is impossible to move without constructing a new object. 
- * If the variable goes out of the scope, stored as a `const reference` inside the expression, 
- * it will be destroyed that will result in a dangling pointer. But this behaviour is helpful 
- * for the construction of an expression because the expression might contain a `const reference` 
- * object that will be passed around as a `const reference` rather than a copy, and we do not need to 
- * construct a whole new chunky object because, under the hood, we are just passing pointers around.
- * 
- */
 protected:
+    /**
+     * @brief This is the only way to discourage the users from using `std::move` on the local 
+     * expression because it works differently from the standard way to move the objects. This weird 
+     * behaviour is due to `const reference`, which is impossible to move without constructing a new object. 
+     * If the variable goes out of the scope, stored as a `const reference` inside the expression, 
+     * it will be destroyed that will result in a dangling pointer. But this behaviour is helpful 
+     * for the construction of an expression because the expression might contain a `const reference` 
+     * object that will be passed around as a `const reference` rather than a copy, and we do not need to 
+     * construct a whole new chunky object because, under the hood, we are just passing pointers around.
+     * 
+     */
     constexpr unary_tensor_expression(unary_tensor_expression&& l) noexcept = default;
 
     /// @brief This the only way to access the protected move constructor of other expressions.