// Purpose: topic overview
// Author: wxWidgets team
// RCS-ID: $Id$
-// Licence: wxWindows license
+// Licence: wxWindows licence
/////////////////////////////////////////////////////////////////////////////
-/*!
+/**
@page overview_refcount Reference Counting
@section overview_refcount_equality Object Comparison
-The == and != operators of the reference counted classes always do a @c deep
-comparison. This means that the equality operator will return @true if two
-objects are identical and not only if they share the same data.
+The == and != operators of @ref overview_refcount_list "the reference counted classes"
+always do a <em>deep comparison</em>. This means that the equality operator
+will return @true if two objects are identical and not only if they share the
+same data.
Note that wxWidgets follows the <em>STL philosophy</em>: when a comparison
-operator can not be implemented efficiently (like for e.g. wxImage's ==
+operator cannot be implemented efficiently (like for e.g. wxImage's ==
operator which would need to compare the entire image's data, pixel-by-pixel),
it's not implemented at all. That's why not all reference counted classes
provide comparison operators.
Also note that if you only need to do a @c shallow comparison between two
-#wxObject derived classes, you should not use the == and != operators but
-rather the wxObject::IsSameAs function.
+wxObject derived classes, you should not use the == and != operators but
+rather the wxObject::IsSameAs() function.
@section overview_refcount_destruct Object Destruction
The following classes in wxWidgets have efficient (i.e. fast) assignment
operators and copy constructors since they are reference-counted:
-@li #wxAcceleratorTable
-@li #wxAnimation
-@li #wxBitmap
-@li #wxBrush
-@li #wxCursor
-@li #wxFont
-@li #wxIcon
-@li #wxImage
-@li #wxMetafile
-@li #wxPalette
-@li #wxPen
-@li #wxRegion
-@li #wxString
-@li #wxVariant
-@li #wxVariantData
+@li wxAcceleratorTable
+@li wxAnimation
+@li wxBitmap
+@li wxBrush
+@li wxCursor
+@li wxFont
+@li wxGraphicsBrush
+@li wxGraphicsContext
+@li wxGraphicsFont
+@li wxGraphicsMatrix
+@li wxGraphicsPath
+@li wxGraphicsPen
+@li wxIcon
+@li wxImage
+@li wxMetafile
+@li wxPalette
+@li wxPen
+@li wxRegion
+@li wxString
+@li wxVariant
+@li wxVariantData
Note that the list above reports the objects which are reference counted in all
ports of wxWidgets; some ports may use this technique also for other classes.
+All the objects implement a function @b IsOk() to test if they are referencing valid
+data; when the objects are in uninitialized state, you can only use the @b IsOk() getter;
+trying to call any other getter, e.g. wxBrush::GetStyle() on the ::wxNullBrush object,
+will result in an assert failure in debug builds.
+
@section overview_refcount_object Making Your Own Reference Counted Class
-Reference counting can be implemented easily using #wxObject and
-#wxObjectRefData classes. Alternatively, you can also use the
-#wxObjectDataPtr<T> template.
+Reference counting can be implemented easily using wxObject or using
+the intermediate wxRefCounter class directly.
+Alternatively, you can also use the wxObjectDataPtr<T> template.
-First, derive a new class from #wxObjectRefData and put there the
-memory-consuming data.
+First, derive a new class from wxRefCounter (or wxObjectRefData when
+using a wxObject derived class) and put the memory-consuming data in it.
-Then derive a new class from #wxObject and implement there the public interface
+Then derive a new class from wxObject and implement there the public interface
which will be seen by the user of your class. You'll probably want to add a
-function to your class which does the cast from #wxObjectRefData to your
+function to your class which does the cast from wxObjectRefData to your
class-specific shared data. For example:
@code
you will need to call this function.
@note Any time you need to actually modify the data placed inside your wxObject
-derived class, you must first call the wxObject::UnShare function to ensure
+derived class, you must first call the wxObject::UnShare() function to ensure
that the modifications won't affect other instances which are eventually
sharing your object's data.