Add checked_cast signatures

Author: reuk

src/util/expr_cast.h

@@ -30,22 +30,24 @@ Author: Nathan Phillips <[email protected]>
 /// \return true if \a base is of type \a T
 template<typename T> bool can_cast_expr(const exprt &base);
 
-/// Called after casting. Provides a point to assert on the structure of the
+/// Called after casting.  Provides a point to assert on the structure of the
 /// expr. By default, this is a no-op, but you can provide an overload to
-/// validate particular types.
+/// validate particular types.  Should always succeed unless the program has
+/// entered an invalid state.  We validate objects at cast time as that is when
+/// these checks have been used historically, but it would be reasonable to
+/// validate objects in this way at any time.
 inline void validate_expr(const exprt &) {}
 
 namespace detail // NOLINT
 {
 
-// We hide this in a namespace so that only functions that it only
-// participates in overload resolution when explicitly requested.
+// We hide these functions in a namespace so that only functions that they only
+// participate in overload resolution when explicitly requested.
 
 /// \brief Try to cast a reference to a generic exprt to a specific derived
 ///    class
 /// \tparam T The reference or const reference type to \a TUnderlying to cast
 ///    to
-/// \tparam TUnderlying An exprt-derived class type
 /// \tparam TExpr The original type to cast from, either exprt or const exprt
 /// \param base Reference to a generic \ref exprt
 /// \return Reference to object of type \a TUnderlying
@@ -54,22 +56,39 @@ template <typename T, typename TExpr>
 optionalt<std::reference_wrapper<typename std::remove_reference<T>::type>>
 expr_try_dynamic_cast(TExpr &base)
 {
-  typedef typename std::decay<T>::type TUnderlying;
-  typedef typename std::remove_reference<T>::type TConst;
+  typedef typename std::decay<T>::type TUnderlyingt;
+  typedef typename std::remove_reference<T>::type TConstt;
   static_assert(
     std::is_same<typename std::remove_const<TExpr>::type, exprt>::value,
     "Tried to expr_try_dynamic_cast from something that wasn't an exprt");
   static_assert(
     std::is_reference<T>::value,
     "Tried to convert exprt & to non-reference type");
   static_assert(
-    std::is_base_of<exprt, TUnderlying>::value,
+    std::is_base_of<exprt, TUnderlyingt>::value,
     "The template argument T must be derived from exprt.");
-  if(!can_cast_expr<TUnderlying>(base))
+  if(!can_cast_expr<TUnderlyingt>(base))
     return {};
-  T value=static_cast<T>(base);
-  validate_expr(value);
-  return std::reference_wrapper<TConst>(value);
+  T ret=static_cast<T>(base);
+  validate_expr(ret);
+  return std::reference_wrapper<TConstt>(ret);
+}
+
+/// \brief Try to cast a reference to a generic exprt to a specific derived
+///    class
+/// \tparam T The reference or const reference type to \a TUnderlying to cast
+///    to
+/// \tparam TExpr The original type to cast from, either exprt or const exprt
+/// \param base Reference to a generic \ref exprt
+/// \return Reference to object of type \a TUnderlying
+///   or valueless optional if \a base is not an instance of \a TUnderlying
+template <typename T, typename TExpr>
+optionalt<std::reference_wrapper<typename std::remove_reference<T>::type>>
+expr_try_checked_cast(TExpr &base)
+{
+  typedef typename std::decay<T>::type TUnderlyingt;
+  PRECONDITION(can_cast_expr<TUnderlyingt>(base));
+  return expr_try_checked_cast<T>(base);
 }
 
 } // namespace detail
@@ -100,40 +119,79 @@ expr_try_dynamic_cast(exprt &base)
   return detail::expr_try_dynamic_cast<T>(base);
 }
 
+/// \brief Try to cast a constant reference to a generic exprt to a specific
+///   derived class. Also assert that the expr invariants are not violated.
+/// \tparam T The exprt-derived class to cast to
+/// \param base Reference to a generic \ref exprt
+/// \return Reference to object of type \a T or valueless optional if \a base
+///   is not an instance of \a T
+template<typename T>
+optionalt<std::reference_wrapper<typename std::remove_reference<T>::type>>
+expr_try_checked_cast(const exprt &base)
+{
+  return detail::expr_try_checked_cast<T>(base);
+}
+
+/// \brief Try to cast a reference to a generic exprt to a specific derived
+///   class. Also assert that the expr invariants are not violated.
+/// \tparam T The exprt-derived class to cast to
+/// \param base Reference to a generic \ref exprt
+/// \return Reference to object of type \a T or valueless optional if \a base is
+///   not an instance of \a T
+template<typename T>
+optionalt<std::reference_wrapper<typename std::remove_reference<T>::type>>
+expr_try_checked_cast(exprt &base)
+{
+  return detail::expr_try_checked_cast<T>(base);
+}
+
 namespace detail // NOLINT
 {
 
-// We hide this in a namespace so that only functions that it only
-// participates in overload resolution when explicitly requested.
+// We hide these functions in a namespace so that only functions that they only
+// participate in overload resolution when explicitly requested.
 
-/// \brief Cast a reference to a generic exprt to a specific derived class
+/// \brief Cast a reference to a generic exprt to a specific derived class.
 /// \tparam T The reference or const reference type to \a TUnderlying to cast to
-/// \tparam TUnderlying An exprt-derived class type
 /// \tparam TExpr The original type to cast from, either exprt or const exprt
 /// \param base Reference to a generic \ref exprt
 /// \return Reference to object of type \a T
 /// \throw std::bad_cast If \a base is not an instance of \a TUnderlying
-/// \remark If CBMC assertions (PRECONDITION) are set to abort then this will
-///   abort rather than throw if \a base is not an instance of \a TUnderlying
 template<typename T, typename TExpr>
 T expr_dynamic_cast(TExpr &base)
 {
-  typedef typename std::decay<T>::type TUnderlying;
+  typedef typename std::decay<T>::type TUnderlyingt;
   static_assert(
     std::is_same<typename std::remove_const<TExpr>::type, exprt>::value,
     "Tried to expr_dynamic_cast from something that wasn't an exprt");
   static_assert(
     std::is_reference<T>::value,
     "Tried to convert exprt & to non-reference type");
   static_assert(
-    std::is_base_of<exprt, TUnderlying>::value,
+    std::is_base_of<exprt, TUnderlyingt>::value,
     "The template argument T must be derived from exprt.");
-  PRECONDITION(can_cast_expr<TUnderlying>(base));
-  if(!can_cast_expr<TUnderlying>(base))
+  if(!can_cast_expr<TUnderlyingt>(base))
     throw std::bad_cast();
-  T value=static_cast<T>(base);
-  validate_expr(value);
-  return value;
+  T ret=static_cast<T>(base);
+  validate_expr(ret);
+  return ret;
+}
+
+/// \brief Cast a reference to a generic exprt to a specific derived class.
+///   Also assert that the expression has the expected type.
+/// \tparam T The reference or const reference type to \a TUnderlying to cast to
+/// \tparam TExpr The original type to cast from, either exprt or const exprt
+/// \param base Reference to a generic \ref exprt
+/// \return Reference to object of type \a T
+/// \throw std::bad_cast If \a base is not an instance of \a TUnderlying
+/// \remark If CBMC assertions (PRECONDITION) are set to abort then this will
+///   abort rather than throw if \a base is not an instance of \a TUnderlying
+template<typename T, typename TExpr>
+T expr_checked_cast(TExpr &base)
+{
+  typedef typename std::decay<T>::type TUnderlyingt;
+  PRECONDITION(can_cast_expr<TUnderlyingt>(base));
+  return expr_dynamic_cast<T>(base);
 }
 
 } // namespace detail
@@ -165,6 +223,34 @@ T expr_dynamic_cast(exprt &base)
   return detail::expr_dynamic_cast<T>(base);
 }
 
+/// \brief Cast a constant reference to a generic exprt to a specific derived
+///   class. Also assert that the exprt invariants are not violated.
+/// \tparam T The exprt-derived class to cast to
+/// \param base Reference to a generic \ref exprt
+/// \return Reference to object of type \a T
+/// \throw std::bad_cast If \a base is not an instance of \a T
+/// \remark If CBMC assertions (PRECONDITION) are set to abort then this will
+///   abort rather than throw if \a base is not an instance of \a T
+template<typename T>
+T expr_checked_cast(const exprt &base)
+{
+  return detail::expr_checked_cast<T>(base);
+}
+
+/// \brief Cast a reference to a generic exprt to a specific derived class.
+///   Also assert that the exprt invariants are not violated.
+/// \tparam T The exprt-derived class to cast to
+/// \param base Reference to a generic \ref exprt
+/// \return Reference to object of type \a T
+/// \throw std::bad_cast If \a base is not an instance of \a T
+/// \remark If CBMC assertions (PRECONDITION) are set to abort then this will
+///   abort rather than throw if \a base is not an instance of \a T
+template<typename T>
+T expr_checked_cast(exprt &base)
+{
+  return detail::expr_checked_cast<T>(base);
+}
+
 inline void validate_operands(
   const exprt &value,
   exprt::operandst::size_type number,