gcc/obstack-utils.h

   1 // Obstack-related utilities.
   2 // Copyright (C) 2020-2021 Free Software Foundation, Inc.
   3 //
   4 // This file is part of GCC.
   5 //
   6 // GCC is free software; you can redistribute it and/or modify it under
   7 // the terms of the GNU General Public License as published by the Free
   8 // Software Foundation; either version 3, or (at your option) any later
   9 // version.
  10 //
  11 // GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 // WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 // FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 // for more details.
  15 //
  16 // You should have received a copy of the GNU General Public License
  17 // along with GCC; see the file COPYING3.  If not see
  18 // <http://www.gnu.org/licenses/>.
  19
  20 #ifndef GCC_OBSTACK_UTILS_H
  21 #define GCC_OBSTACK_UTILS_H
  22
  23 // This RAII class automatically frees memory allocated on an obstack,
  24 // unless told not to via keep ().  It automatically converts to an
  25 // obstack, so it can (optionally) be used in place of the obstack
  26 // to make the scoping clearer.  For example:
  27 //
  28 //     obstack_watermark watermark (ob);
  29 //     auto *ptr1 = XOBNEW (watermark, struct1);
  30 //     if (...)
  31 //       // Frees ptr1.
  32 //       return false;
  33 //
  34 //     auto *ptr2 = XOBNEW (watermark, struct2);
  35 //     if (...)
  36 //       // Frees ptr1 and ptr2.
  37 //       return false;
  38 //
  39 //     // Retains ptr1 and ptr2.
  40 //     watermark.keep ();
  41 //
  42 //     auto *ptr3 = XOBNEW (watermark, struct3);
  43 //     if (...)
  44 //       // Frees ptr3.
  45 //       return false;
  46 //
  47 //     // Retains ptr3 (in addition to ptr1 and ptr2 above).
  48 //     watermark.keep ();
  49 //     return true;
  50 //
  51 // The move constructor makes it possible to transfer ownership to a caller:
  52 //
  53 //     obstack_watermark
  54 //     foo ()
  55 //     {
  56 //       obstack_watermark watermark (ob);
  57 //       ...
  58 //       return watermark;
  59 //     }
  60 //
  61 //     void
  62 //     bar ()
  63 //     {
  64 //       // Inherit ownership of everything that foo allocated.
  65 //       obstack_watermark watermark = foo ();
  66 //       ...
  67 //     }
  68 class obstack_watermark
  69 {
  70 public:
  71   obstack_watermark (obstack *ob) : m_obstack (ob) { keep (); }
  72   constexpr obstack_watermark (obstack_watermark &&) = default;
  73   ~obstack_watermark () { obstack_free (m_obstack, m_start); }
  74
  75   operator obstack *() const { return m_obstack; }
  76   void keep () { m_start = XOBNEWVAR (m_obstack, char, 0); }
  77
  78 private:
  79   DISABLE_COPY_AND_ASSIGN (obstack_watermark);
  80
  81 protected:
  82   obstack *m_obstack;
  83   char *m_start;
  84 };
  85
  86 #endif