layout/generic/nsQueryFrame.h

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #ifndef nsQueryFrame_h
   6 #define nsQueryFrame_h
   7
   8 #include "nscore.h"
   9 #include "mozilla/Assertions.h"
  10 #include "mozilla/TypeTraits.h"
  11
  12 // NOTE: the long lines in this file are intentional to make compiler error
  13 // messages more readable.
  14
  15 #define NS_DECL_QUERYFRAME_TARGET(classname)                    \
  16   static const nsQueryFrame::FrameIID kFrameIID = nsQueryFrame::classname##_id; \
  17   typedef classname Has_NS_DECL_QUERYFRAME_TARGET;
  18
  19 #define NS_DECL_QUERYFRAME                                      \
  20   virtual void* QueryFrame(FrameIID id);
  21
  22 #define NS_QUERYFRAME_HEAD(class)                               \
  23   void* class::QueryFrame(FrameIID id) { switch (id) {
  24
  25 #define NS_QUERYFRAME_ENTRY(class)                              \
  26   case class::kFrameIID: {                                      \
  27     static_assert(mozilla::IsSame<class, class::Has_NS_DECL_QUERYFRAME_TARGET>::value, \
  28                   #class " must declare itself as a queryframe target"); \
  29     return static_cast<class*>(this);                           \
  30   }
  31
  32 #define NS_QUERYFRAME_ENTRY_CONDITIONAL(class, condition)       \
  33   case class::kFrameIID:                                        \
  34   if (condition) {                                              \
  35     static_assert(mozilla::IsSame<class, class::Has_NS_DECL_QUERYFRAME_TARGET>::value, \
  36                   #class " must declare itself as a queryframe target"); \
  37     return static_cast<class*>(this);                           \
  38   }                                                             \
  39   break;
  40
  41 #define NS_QUERYFRAME_TAIL_INHERITING(class)                    \
  42   default: break;                                               \
  43   }                                                             \
  44   return class::QueryFrame(id);                                 \
  45 }
  46
  47 #define NS_QUERYFRAME_TAIL_INHERITANCE_ROOT                     \
  48   default: break;                                               \
  49   }                                                             \
  50   MOZ_ASSERT(id != GetFrameId(),                                \
  51     "A frame failed to QueryFrame to its *own type*. "          \
  52     "It may be missing NS_DECL_QUERYFRAME, or a "               \
  53     "NS_QUERYFRAME_ENTRY() line with its own type name");       \
  54   return nullptr;                                               \
  55 }
  56
  57 class nsQueryFrame
  58 {
  59 public:
  60   enum FrameIID {
  61 #define FRAME_ID(classname) classname##_id,
  62 #include "nsFrameIdList.h"
  63 #undef FRAME_ID
  64
  65     // The PresArena implementation uses this bit to distinguish objects
  66     // allocated by size from objects allocated by type ID (that is, frames
  67     // using AllocateByFrameID, and other objects using AllocateByObjectID).
  68     // It should not collide with any frame ID (above) or Object ID (in
  69     // nsPresArena.h).  It is not 0x80000000 to avoid the question of
  70     // whether enumeration constants are signed.
  71     NON_FRAME_MARKER = 0x20000000
  72   };
  73
  74   virtual void* QueryFrame(FrameIID id) = 0;
  75 };
  76
  77 class do_QueryFrame
  78 {
  79 public:
  80   explicit do_QueryFrame(nsQueryFrame *s) : mRawPtr(s) { }
  81
  82   // The return and argument types here are arbitrarily selected so no
  83   // corresponding member function exists.
  84   typedef void (do_QueryFrame::* MatchNullptr)(double, float);
  85   // Implicit constructor for nullptr, trick borrowed from already_AddRefed.
  86   MOZ_IMPLICIT do_QueryFrame(MatchNullptr aRawPtr) : mRawPtr(nullptr) {}
  87
  88   template<class Dest>
  89   operator Dest*() {
  90     static_assert(mozilla::IsSame<Dest, typename Dest::Has_NS_DECL_QUERYFRAME_TARGET>::value,
  91                   "Dest must declare itself as a queryframe target");
  92     if (!mRawPtr)
  93       return nullptr;
  94
  95     return reinterpret_cast<Dest*>(mRawPtr->QueryFrame(Dest::kFrameIID));
  96   }
  97
  98 private:
  99   nsQueryFrame *mRawPtr;
 100 };
 101
 102 #endif // nsQueryFrame_h