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60 lines
2.1 KiB
Objective-C
60 lines
2.1 KiB
Objective-C
//
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// ASWeakMap.h
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// AsyncDisplayKit
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//
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// Created by Chris Danford on 7/11/16.
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//
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// Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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//
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#import <Foundation/Foundation.h>
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NS_ASSUME_NONNULL_BEGIN
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/**
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* This class is used in conjunction with ASWeakMap. Instances of this type are returned by an ASWeakMap,
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* must retain this value for as long as they want the entry to exist in the map.
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*/
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@interface ASWeakMapEntry<Value> : NSObject
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@property (nonatomic, retain, readonly) Value value;
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@end
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/**
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* This is not a full-featured map. It does not support features like `count` and FastEnumeration because there
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* is not currently a need.
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*
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* This is a map that does not retain keys or values added to it. When both getting and setting, the caller is
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* returned a ASWeakMapEntry and must retain it for as long as it wishes the key/value to remain in the map.
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* We return a single Entry value to the caller to avoid two potential problems:
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*
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* 1) It's easier for callers to retain one value (the Entry) and not two (a key and a value).
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* 2) Key values are tested for `isEqual` equality. If if a caller asks for a key "A" that is equal to a key "B"
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* already in the map, then we need the caller to retain key "B" and not key "A". Returning an Entry simplifies
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* the semantics.
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*
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* The underlying storage is a hash table and the Key type should implement `hash` and `isEqual:`.
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*/
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@interface ASWeakMap<__covariant Key : NSObject *, Value> : NSObject
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/**
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* Read from the cache. The Value object is accessible from the returned ASWeakMapEntry.
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*/
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- (nullable ASWeakMapEntry<Value> *)entryForKey:(Key)key;
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/**
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* Put a value into the cache. If an entry with an equal key already exists, then the value is updated on the existing entry.
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*/
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- (ASWeakMapEntry<Value> *)setObject:(Value)value forKey:(Key)key;
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@end
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NS_ASSUME_NONNULL_END
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