Return pointer from expr_try_dynamic_cast

Author: reuk

src/util/expr_cast.h

@@ -18,7 +18,6 @@ Author: Nathan Phillips <Nathan.Phillips@diffblue.com>
 
 #include "invariant.h"
 #include "expr.h"
-#include "optional.h"
 
 /// \brief Check whether a reference to a generic \ref exprt is of a specific
 ///   derived class.
@@ -41,71 +40,70 @@ inline void validate_expr(const exprt &) {}
 namespace detail // NOLINT
 {
 
-// We hide these functions in a namespace so that they only participate in
-// overload resolution when explicitly requested.
+template<typename Ret, typename T>
+struct expr_try_dynamic_cast_return_typet final
+{
+  static_assert(
+    !std::is_reference<Ret>::value,
+    "Ret must be non-qualified");
+
+  typedef
+    typename std::conditional<
+      std::is_const<T>::value,
+      typename std::add_const<Ret>::type,
+      Ret>::type *
+    type;
+};
+
+} // namespace detail
 
 /// \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
+/// \return Ptr to object of type \a TUnderlying
+///   or nullptr 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_dynamic_cast(TExpr &base)
+auto expr_try_dynamic_cast(TExpr &base)
+  -> typename detail::expr_try_dynamic_cast_return_typet<T, TExpr>::type
 {
-  typedef typename std::decay<T>::type decayt;
+  typedef
+    typename detail::expr_try_dynamic_cast_return_typet<T, TExpr>::type
+    returnt;
   static_assert(
-    std::is_same<typename std::remove_const<TExpr>::type, exprt>::value,
+    std::is_same<typename std::decay<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, decayt>::value,
+    std::is_base_of<exprt, T>::value,
     "The template argument T must be derived from exprt.");
-  if(!can_cast_expr<decayt>(base))
-    return {};
-  T ret=static_cast<T>(base);
-  validate_expr(ret);
-  return std::reference_wrapper<typename std::remove_reference<T>::type>(ret);
+  if(!can_cast_expr<T>(base))
+    return nullptr;
+  const auto ret=static_cast<returnt>(&base);
+  validate_expr(*ret);
+  return ret;
 }
 
-} // namespace detail
-
-/// \brief Try to cast a constant reference to a generic exprt to a specific
-///   derived class
-/// \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_dynamic_cast(const exprt &base)
+namespace detail // NOLINT
 {
-  return detail::expr_try_dynamic_cast<T>(base);
-}
 
-/// \brief Try to cast a reference to a generic exprt to a specific derived
-///   class
-/// \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_dynamic_cast(exprt &base)
+template<typename Ret, typename T>
+struct expr_dynamic_cast_return_typet final
 {
-  return detail::expr_try_dynamic_cast<T>(base);
-}
+  static_assert(
+    !std::is_reference<Ret>::value,
+    "Ret must be non-qualified");
 
-namespace detail // NOLINT
-{
+  typedef
+    typename std::conditional<
+      std::is_const<T>::value,
+      typename std::add_const<Ret>::type,
+      Ret>::type &
+    type;
+};
 
-// We hide these functions in a namespace so that they only participate in
-// overload resolution when explicitly requested.
+} // namespace detail
 
 /// \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
@@ -114,23 +112,13 @@ namespace detail // NOLINT
 /// \return Reference to object of type \a T
 /// \throw std::bad_cast If \a base is not an instance of \a TUnderlying
 template<typename T, typename TExpr>
-T expr_dynamic_cast(TExpr &base)
+auto expr_dynamic_cast(TExpr &base)
+  -> typename detail::expr_dynamic_cast_return_typet<T, TExpr>::type
 {
-  typedef typename std::decay<T>::type decayt;
-  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, decayt>::value,
-    "The template argument T must be derived from exprt.");
-  if(!can_cast_expr<decayt>(base))
+  const auto ret=expr_try_dynamic_cast<T>(base);
+  if(ret==nullptr)
     throw std::bad_cast();
-  T ret=static_cast<T>(base);
-  validate_expr(ret);
-  return ret;
+  return *ret;
 }
 
 /// \brief Cast a reference to a generic exprt to a specific derived class.
@@ -143,69 +131,13 @@ T expr_dynamic_cast(TExpr &base)
 /// \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)
+auto expr_checked_cast(TExpr &base)
+  -> typename detail::expr_dynamic_cast_return_typet<T, TExpr>::type
 {
-  PRECONDITION(can_cast_expr<typename std::decay<T>::type>(base));
+  PRECONDITION(can_cast_expr<T>(base));
   return expr_dynamic_cast<T>(base);
 }
 
-} // namespace detail
-
-/// \brief Cast a constant reference to a generic exprt to a specific derived
-///   class
-/// \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_dynamic_cast(const exprt &base)
-{
-  return detail::expr_dynamic_cast<T>(base);
-}
-
-/// \brief Cast a reference to a generic exprt to a specific derived class
-/// \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_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,

src/util/std_code.h

@@ -55,7 +55,7 @@ inline bool can_cast_code_impl(const exprt &expr, const Tag &tag)
 {
   try
   {
-    return expr_dynamic_cast<const codet &>(expr).get_statement()==tag;
+    return expr_dynamic_cast<codet>(expr).get_statement()==tag;
   }
   catch(const std::bad_cast &)
   {
@@ -1246,8 +1246,7 @@ inline bool can_cast_side_effect_expr_impl(const exprt &expr, const Tag &tag)
 {
   try
   {
-    return
-      expr_dynamic_cast<const side_effect_exprt &>(expr).get_statement()==tag;
+    return expr_dynamic_cast<side_effect_exprt>(expr).get_statement()==tag;
   }
   catch(const std::bad_cast &)
   {

unit/util/expr_cast/expr_cast.cpp

@@ -23,12 +23,12 @@ SCENARIO("expr_dynamic_cast",
     THEN("Try-casting from exprt reference to symbol_exprt pointer "
          "returns a value")
     {
-      REQUIRE(expr_try_dynamic_cast<const symbol_exprt &>(expr).has_value());
+      REQUIRE(expr_try_dynamic_cast<symbol_exprt>(expr)!=nullptr);
     }
 
     THEN("Casting from exprt pointer to transt pointer doesn't return a value")
     {
-      REQUIRE(!expr_try_dynamic_cast<const transt &>(expr).has_value());
+      REQUIRE(expr_try_dynamic_cast<transt>(expr)==nullptr);
     }
   }
   GIVEN("A exprt reference to a symbolt")
@@ -38,13 +38,13 @@ SCENARIO("expr_dynamic_cast",
     THEN("Casting from exprt reference to symbol_exprt reference "
          "returns a value")
     {
-      REQUIRE(expr_try_dynamic_cast<symbol_exprt &>(expr).has_value());
+      REQUIRE(expr_try_dynamic_cast<symbol_exprt>(expr)!=nullptr);
     }
 
     THEN("Casting from exprt reference to transt reference "
          "doesn't return a value")
     {
-      REQUIRE(!expr_try_dynamic_cast<transt &>(expr).has_value());
+      REQUIRE(expr_try_dynamic_cast<transt>(expr)==nullptr);
     }
   }
   GIVEN("A const exprt reference to a symbolt")
@@ -54,15 +54,15 @@ SCENARIO("expr_dynamic_cast",
     THEN(
       "Casting from exprt reference to symbol_exprt reference should not throw")
     {
-      REQUIRE_NOTHROW(expr_dynamic_cast<const symbol_exprt &>(expr_ref));
+      REQUIRE_NOTHROW(expr_dynamic_cast<symbol_exprt>(expr_ref));
     }
 
     THEN("Casting from exprt reference to transt reference should throw")
     {
       // This no longer throws exceptions when our custom asserts are set to
       //  abort the program
       // REQUIRE_THROWS_AS(
-      //   expr_dynamic_cast<const transt &>(expr_ref),
+      //   expr_dynamic_cast<transt>(expr_ref),
       //   std::bad_cast);
     }
   }
@@ -73,23 +73,23 @@ SCENARIO("expr_dynamic_cast",
     THEN(
       "Casting from exprt reference to symbol_exprt reference should not throw")
     {
-      REQUIRE_NOTHROW(expr_dynamic_cast<symbol_exprt &>(expr_ref));
+      REQUIRE_NOTHROW(expr_dynamic_cast<symbol_exprt>(expr_ref));
     }
 
     THEN("Casting from exprt reference to transt reference should throw")
     {
       // This no longer throws exceptions when our custom asserts are set to
       //  abort the program
       // REQUIRE_THROWS_AS(
-      //   expr_dynamic_cast<transt &>(expr_ref),
+      //   expr_dynamic_cast<transt>(expr_ref),
       //   std::bad_cast);
     }
 
     THEN(
       "Casting from non-const exprt reference to const symbol_exprt reference "
       "should be fine")
     {
-      REQUIRE_NOTHROW(expr_dynamic_cast<const symbol_exprt &>(expr_ref));
+      REQUIRE_NOTHROW(expr_dynamic_cast<symbol_exprt>(expr_ref));
     }
   }
 }