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54 lines
No EOL
2.3 KiB
Objective-C
54 lines
No EOL
2.3 KiB
Objective-C
/** Key-Value Coding Safe Caching Support
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Copyright (C) 2024 Free Software Foundation, Inc.
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Written by: Hugo Melder <hugo@algoriddim.com>
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Created: August 2024
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This file is part of the GNUstep Base Library.
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free
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Software Foundation, Inc., 31 Milk Street #960789 Boston, MA 02196 USA.
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*/
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/**
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* It turns out that valueForKey: is a very expensive operation, and a major
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* bottleneck for Key-Value Observing and other operations such as sorting
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* an array by key.
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*
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* The accessor search patterns for Key-Value observing are discussed in the
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* Apple Key-Value Coding Programming Guide. The return value may be
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* encapuslated into an NSNumber or NSValue object, depending on the Objective-C
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* type encoding of the return value. This means that once valueForKey: found an
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* existing accessor, the Objective-C type encoding of the accessor is
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* retrieved. We then go through a huge switch case to determine the right way
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* to invoke the IMP and potentially encapsulate the return type. The resulting
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* object is then returned.
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* The algorithm for setValue:ForKey: is similar.
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*
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* We can speed this up by caching the IMP of the accessor in a hash table.
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* However, without proper versioning, this quickly becomes very dangerous.
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* The user might exchange implementations, or add new ones expecting the
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* search pattern invariant to still hold. If we clamp onto an IMP, this
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* invariant no longer holds.
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*
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* We will make use of libobjc2's safe caching to avoid this.
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*
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* Note that the caching is opaque. You will only need to redirect all
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* valueForKey: calls to the function below.
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*/
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#import "Foundation/NSString.h"
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id
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valueForKeyWithCaching(id obj, NSString *aKey); |