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#if !defined(INCLUDED_GSUNIQUED)
#define INCLUDED_GSUNIQUED 1
/**
Copyright (C) 2014 Free Software Foundation, Inc.
Written by: Richard Frith-Macdonald <rfm@gnu.org>
Date: April 2014
This file is part of the Performance Library.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 3 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111 USA.
*/
#import <Foundation/NSObject.h>
/** Class used to unique other objects.<br />
* <p>The point of this class is to lower the memory footprint and speed
* up comparisons (pointer equality) in cases where an application
* stores multiple copies of the same object in various maps.<br />
* Since uniquing is performed by storing an immutable copy of the
* original object in a map until there are no further references
* to that object, it's pointless to use this uniquing unless the
* application would be storing at least two copies of the object.<br />
* Also, since this is thread-safe there is a lock management
* overhead wherever a uniqued object is released, so performance
* gains are to be expected only if the uniqued object has a
* relatively long lifetime and is tested for equality with other
* instances frequently.<br />
* In short, use with care; while uniquing can have a big performance
* advantage for some programs, this is actually quite rare.
* </p>
* <p>The internal implementation of the uniquing works by taking
* immutable copies of the objects to be uniqued, storing those copies
* in a hash table, and swizzling their class pointers to a sub-class
* which will automatically remove the instance from the hash table
* before it is deallocated.<br />
* Access to the hash table is protected by locks so that uniqued
* objects may be used freely in multiple threads.<br />
* The name of the subclass used is the name of the original class
* with 'GSUniqued' added as a prefix.
* </p>
*/
@interface GSUniqued : NSObject
/** This method returns a copy of its argument, uniqued so that other
* such copies of equal objects will be the same instance.<br />
* The argument must respond to -copyWithZone: by returning an instance
* of class of immutable objects (ie where the -hash and -isEqual:
* methods are stable for that instance).
*/
+ (id) copyUniqued: (id<NSObject,NSCopying>)anObject;
@end
/** Category for uniquing any copyable object.<br />
* NB. This must only be used by classes for which -copyWithZone:
* produces an instance of an immutable class.
*/
@interface NSObject (GSUniqued)
/** This method returns a copy of the receiver uniqued so that other
* such copies of equal objects content will be the same instance.
*/
- (id) copyUniqued;
@end
#endif
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