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      1 /* Copyright (C) 2022-2024 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_STATIC_CAST_H
     19 #define COMMON_GDB_CHECKED_STATIC_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   gdb_assert (v == nullptr || dynamic_cast<T> (v) != nullptr);
     58 #endif
     59 
     60   /* If a base class of V is virtual then the dynamic_cast above will
     61      succeed, but this static_cast will fail.  */
     62   return static_cast<T> (v);
     63 }
     64 
     65 /* Same as the above, but to cast from a reference type to another.  */
     66 
     67 template<typename T, typename V, typename = gdb::Requires<std::is_reference<T>>>
     68 T
     69 checked_static_cast (V &v)
     70 {
     71   static_assert (std::is_reference<T>::value, "target must be a reference type");
     72 
     73   using T_no_R = typename std::remove_reference<T>::type;
     74   using T_P = typename std::add_pointer<T_no_R>::type;
     75 
     76   using V_no_R = typename std::remove_reference<V>::type;
     77 
     78   return *checked_static_cast<T_P, V_no_R> (&v);
     79 }
     80 
     81 }
     82 
     83 #endif /* COMMON_GDB_CHECKED_STATIC_CAST_H */
     84