AsyncDisplayKit/AsyncDisplayKit/Private/ASWeakMap.h at master · HackPlan/AsyncDisplayKit · GitHub

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// ASWeakMap.h

// AsyncDisplayKit

// Created by Chris Danford on 7/11/16.

// This source code is licensed under the BSD-style license found in the

// LICENSE file in the root directory of this source tree. An additional grant

// of patent rights can be found in the PATENTS file in the same directory.

#import <Foundation/Foundation.h>

#import <AsyncDisplayKit/ASBaseDefines.h>

NS_ASSUME_NONNULL_BEGIN

/**

* This class is used in conjunction with ASWeakMap. Instances of this type are returned by an ASWeakMap,

* must retain this value for as long as they want the entry to exist in the map.

@interface ASWeakMapEntry<Value> : NSObject

@property (nonatomic, retain, readonly) Value value;

@end

/**

* This is not a full-featured map. It does not support features like `count` and FastEnumeration because there

* is not currently a need.

* This is a map that does not retain keys or values added to it. When both getting and setting, the caller is

* returned a ASWeakMapEntry and must retain it for as long as it wishes the key/value to remain in the map.

* We return a single Entry value to the caller to avoid two potential problems:

* 1) It's easier for callers to retain one value (the Entry) and not two (a key and a value).

* 2) Key values are tested for `isEqual` equality. If if a caller asks for a key "A" that is equal to a key "B"

* already in the map, then we need the caller to retain key "B" and not key "A". Returning an Entry simplifies

* the semantics.

* The underlying storage is a hash table and the Key type should implement `hash` and `isEqual:`.

@interface ASWeakMap<__covariant Key : NSObject *, Value> : NSObject

/**

* Read from the cache. The Value object is accessible from the returned ASWeakMapEntry.

- (nullable ASWeakMapEntry<Value> *)entryForKey:(Key)key AS_WARN_UNUSED_RESULT;

/**

* Put a value into the cache. If an entry with an equal key already exists, then the value is updated on the existing entry.

- (ASWeakMapEntry<Value> *)setObject:(Value)value forKey:(Key)key AS_WARN_UNUSED_RESULT;

@end

NS_ASSUME_NONNULL_END

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