Extract "external field" approach in a reusable class

Add wxExternalField<> template that can be used for other fields and/or
in other ports too.

include/wx/private/extfield.h

@@ -0,0 +1,84 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/private/extfield.h
+// Purpose:     Declare wxExternalField helper
+// Author:      Vadim Zeitlin
+// Created:     2017-11-21
+// Copyright:   (c) 2017 Vadim Zeitlin <vadim@wxwidgets.org>
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_PRIVATE_EXTFIELD_H_
+#define _WX_PRIVATE_EXTFIELD_H_
+
+// ----------------------------------------------------------------------------
+// wxExternalField: store object data outside of it
+// ----------------------------------------------------------------------------
+
+// This class allows to store some data without consuming space for the objects
+// that don't need it and can be useful for avoiding to add rarely used fields
+// to the classes that are used by many objects, e.g. wxWindow.
+//
+// Note that using this class costs in speed and convenience of access to the
+// field, which requires a hash lookup instead of accessing it directly. It
+// also only currently works for heap-allocated fields as it's probably never
+// worth using it for fields of simple types.
+//
+// Template parameter Object is the class that "contains" the field, Field is
+// the type of the field itself and FieldMap is the hash map, defined
+// separately using WX_DECLARE_HASH_MAP(), with Object* as the key and Field*
+// as the value type.
+template <typename Object, typename Field, typename FieldMap>
+class wxExternalField
+{
+public:
+    typedef Object ObjectType;
+    typedef Field FieldType;
+    typedef FieldMap MapType;
+
+    // Store the field object to be used for the given object, replacing the
+    // existing one, if any.
+    //
+    // This method takes ownership of the field pointer which will be destroyed
+    // by EraseForWindow().
+    static void StoreForWindow(ObjectType* obj, FieldType* field)
+    {
+        const typename MapType::iterator it = ms_map.find(obj);
+        if ( it != ms_map.end() )
+        {
+            delete it->second;
+            it->second = field;
+        }
+        else
+        {
+            ms_map.insert(typename MapType::value_type(obj, field));
+        }
+    }
+
+    // Find the object for the corresponding window.
+    static FieldType* FromWindow(ObjectType* obj)
+    {
+        const typename MapType::const_iterator it = ms_map.find(obj);
+        return it == ms_map.end() ? NULL : it->second;
+    }
+
+    // Erase the object used for the corresponding window, return true if there
+    // was one or false otherwise.
+    static bool EraseForWindow(ObjectType* obj)
+    {
+        const typename MapType::iterator it = ms_map.find(obj);
+        if ( it == ms_map.end() )
+            return false;
+
+        delete it->second;
+        ms_map.erase(it);
+        return true;
+    }
+
+private:
+    static FieldMap ms_map;
+};
+
+template <typename O, typename F, typename M>
+M wxExternalField<O, F, M>::ms_map;
+
+#endif // _WX_PRIVATE_EXTFIELD_H_

src/osx/cocoa/window.mm

@@ -24,7 +24,6 @@
 #endif
 
 #include "wx/evtloop.h"
-#include "wx/hashmap.h"
 
 #if wxUSE_CARET
     #include "wx/caret.h"
@@ -1502,11 +1501,6 @@ void wxWidgetCocoaImpl::keyEvent(WX_NSEvent event, WXWidget slf, void *_cmd)
 
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_10
 
-class wxCocoaGesturesImpl;
-WX_DECLARE_HASH_MAP(wxWidgetCocoaImpl*, wxCocoaGesturesImpl*,
-                    wxPointerHash, wxPointerEqual,
-                    wxCocoaGesturesImplMap);
-
 // Class containing data used for gestures support.
 class wxCocoaGesturesImpl
 {
@@ -1602,58 +1596,11 @@ public:
         [m_initialTouch release];
     }
 
-    // We keep all existing wxCocoaGesturesImpl objects in a
-    // wxWidgetCocoaImpl-indexed map. We do this instead of just having a data
-    // member containing wxCocoaGesturesImpl pointer in wxWidgetCocoaImpl
-    // itself because most windows don't need it and it seems wasteful to
-    // always increase their size unnecessarily.
-
-    // Store the object to be used for the given window, replacing the existing
-    // one, if any.
-    //
-    // This method takes ownership of wxCocoaGesturesImpl pointer which will be
-    // destroyed by EraseForWindow().
-    static void StoreForWindow(wxWidgetCocoaImpl* impl, wxCocoaGesturesImpl* obj)
-    {
-        const wxCocoaGesturesImplMap::iterator it = ms_map.find(impl);
-        if ( it != ms_map.end() )
-        {
-            delete it->second;
-            it->second = obj;
-        }
-        else
-        {
-            ms_map.insert(wxCocoaGesturesImplMap::value_type(impl, obj));
-        }
-    }
-
-    // Find the object for the corresponding window.
-    static wxCocoaGesturesImpl* FromWindow(wxWidgetCocoaImpl* impl)
-    {
-        const wxCocoaGesturesImplMap::const_iterator it = ms_map.find(impl);
-        return it == ms_map.end() ? NULL : it->second;
-    }
-
-    // Erase the object used for the corresponding window, return true if there
-    // was one or false otherwise.
-    static bool EraseForWindow(wxWidgetCocoaImpl* impl)
-    {
-        const wxCocoaGesturesImplMap::iterator it = ms_map.find(impl);
-        if ( it == ms_map.end() )
-            return false;
-
-        delete it->second;
-        ms_map.erase(it);
-        return true;
-    }
-
     void TouchesBegan(NSEvent* event);
     void TouchesMoved(NSEvent* event);
     void TouchesEnded(NSEvent* event);
 
 private:
-    static wxCocoaGesturesImplMap ms_map;
-
     wxWindowMac* const m_win;
     NSView* const m_view;
 
@@ -1673,7 +1620,21 @@ private:
     wxDECLARE_NO_COPY_CLASS(wxCocoaGesturesImpl);
 };
 
-wxCocoaGesturesImplMap wxCocoaGesturesImpl::ms_map;
+// We keep all existing wxCocoaGesturesImpl objects in a
+// wxWidgetCocoaImpl-indexed map. We do this instead of just having a data
+// member containing wxCocoaGesturesImpl pointer in wxWidgetCocoaImpl
+// itself because most windows don't need it and it seems wasteful to
+// always increase their size unnecessarily.
+
+#include "wx/hashmap.h"
+WX_DECLARE_HASH_MAP(wxWidgetCocoaImpl*, wxCocoaGesturesImpl*,
+                    wxPointerHash, wxPointerEqual,
+                    wxCocoaGesturesImplMap);
+
+#include "wx/private/extfield.h"
+typedef wxExternalField<wxWidgetCocoaImpl,
+                        wxCocoaGesturesImpl,
+                        wxCocoaGesturesImplMap> wxCocoaGestures;
 
 void wxWidgetCocoaImpl::PanGestureEvent(NSPanGestureRecognizer* panGestureRecognizer)
 {
@@ -1875,7 +1836,7 @@ enum TrackedGestures
 
 void wxWidgetCocoaImpl::TouchesBegan(WX_NSEvent event)
 {
-    if ( wxCocoaGesturesImpl* gestures = wxCocoaGesturesImpl::FromWindow(this) )
+    if ( wxCocoaGesturesImpl* gestures = wxCocoaGestures::FromWindow(this) )
         gestures->TouchesBegan(event);
 }
 
@@ -1932,7 +1893,7 @@ void wxCocoaGesturesImpl::TouchesBegan(NSEvent* event)
 
 void wxWidgetCocoaImpl::TouchesMoved(WX_NSEvent event)
 {
-    if ( wxCocoaGesturesImpl* gestures = wxCocoaGesturesImpl::FromWindow(this) )
+    if ( wxCocoaGesturesImpl* gestures = wxCocoaGestures::FromWindow(this) )
         gestures->TouchesMoved(event);
 }
 
@@ -1988,7 +1949,7 @@ void wxCocoaGesturesImpl::TouchesMoved(NSEvent* event)
 
 void wxWidgetCocoaImpl::TouchesEnded(WX_NSEvent event)
 {
-    if ( wxCocoaGesturesImpl* gestures = wxCocoaGesturesImpl::FromWindow(this) )
+    if ( wxCocoaGesturesImpl* gestures = wxCocoaGestures::FromWindow(this) )
         gestures->TouchesEnded(event);
 }
 
@@ -2540,7 +2501,7 @@ wxWidgetCocoaImpl::~wxWidgetCocoaImpl()
         CFRelease(m_osxView);
 
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_10
-    wxCocoaGesturesImpl::EraseForWindow(this);
+    wxCocoaGestures::EraseForWindow(this);
 #endif // MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_10
 }
 
@@ -3469,7 +3430,7 @@ bool wxWidgetCocoaImpl::EnableTouchEvents(int eventsMask)
         {
             if ( eventsMask == wxTOUCH_NONE )
             {
-                if ( wxCocoaGesturesImpl::EraseForWindow(this) )
+                if ( wxCocoaGestures::EraseForWindow(this) )
                 {
                     [m_osxView setAcceptsTouchEvents:NO];
                 }
@@ -3477,7 +3438,7 @@ bool wxWidgetCocoaImpl::EnableTouchEvents(int eventsMask)
             }
             else // We do want to have gesture events.
             {
-                wxCocoaGesturesImpl::StoreForWindow
+                wxCocoaGestures::StoreForWindow
                 (
                     this,
                     new wxCocoaGesturesImpl(this, m_osxView, eventsMask)