gdbsupport/gdb-checked-static-cast.h

   1 /* Copyright (C) 2022-2023 Free Software Foundation, Inc.
   2
   3    This file is part of GDB.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  17
  18 #ifndef COMMON_GDB_CHECKED_DYNAMIC_CAST_H
  19 #define COMMON_GDB_CHECKED_DYNAMIC_CAST_H
  20
  21 #include "gdbsupport/traits.h"
  22
  23 namespace gdb
  24 {
  25
  26 /* This function can be used in place of static_cast when casting between
  27    pointers of polymorphic types.  The benefit of using this call is that,
  28    when compiling in developer mode, dynamic_cast will be used to validate
  29    the cast.  This use of dynamic_cast is why this function will only
  30    work for polymorphic types.
  31
  32    In non-developer (i.e. production) builds, the dynamic_cast is replaced
  33    with a static_cast which is usually significantly faster.  */
  34
  35 template<typename T, typename V>
  36 T
  37 checked_static_cast (V *v)
  38 {
  39   /* We only support casting to pointer types.  */
  40   static_assert (std::is_pointer<T>::value, "target must be a pointer type");
  41
  42   /* Check for polymorphic types explicitly in case we're in release mode.  */
  43   static_assert (std::is_polymorphic<V>::value, "types must be polymorphic");
  44
  45   /* Figure out the type that T points to.  */
  46   using T_no_P = typename std::remove_pointer<T>::type;
  47
  48   /* In developer mode this cast uses dynamic_cast to confirm at run-time
  49      that the cast from V* to T is valid.  However, we can catch some
  50      mistakes at compile time, this assert prevents anything other than
  51      downcasts, or casts to same type.  */
  52   static_assert (std::is_base_of<V, T_no_P>::value
  53                  || std::is_base_of<T_no_P, V>::value,
  54                  "types must be related");
  55
  56 #ifdef DEVELOPMENT
  57   if (v == nullptr)
  58     return nullptr;
  59
  60   T result = dynamic_cast<T> (v);
  61   gdb_assert (result != nullptr);
  62 #else
  63   T result = static_cast<T> (v);
  64 #endif
  65
  66   return result;
  67 }
  68
  69 /* Same as the above, but to cast from a reference type to another.  */
  70
  71 template<typename T, typename V, typename = gdb::Requires<std::is_reference<T>>>
  72 T
  73 checked_static_cast (V &v)
  74 {
  75   static_assert (std::is_reference<T>::value, "target must be a reference type");
  76
  77   using T_no_R = typename std::remove_reference<T>::type;
  78   using T_P = typename std::add_pointer<T_no_R>::type;
  79
  80   using V_no_R = typename std::remove_reference<V>::type;
  81
  82   return *checked_static_cast<T_P, V_no_R> (&v);
  83 }
  84
  85 }
  86
  87 #endif /* COMMON_GDB_CHECKED_DYNAMIC_CAST_H */