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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,59 @@ | ||
| # WeakDictionary | ||
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| ## Functionality | ||
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| A `WeakDictionary` is a dictionary holding weak references onto its values. It may be useful in similar areas as `WeakArray` or `WeakSet`: Everywhere, where only weak references to the dictionary values should be kept, so if the retain count of a value stored in the dictionary becomes zero, the value for the corresponding key gets removed. | ||
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| ## Implementation | ||
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| A `WeakDictionary` is a generic type with Key and Value both conforming to `Hashable`. Itself, it conforms to | ||
| - `CustomStringConvertible`, | ||
| - `ExpressibleByDictionaryLiteral`, | ||
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| Internally, `WeakDictionary` stores a `Dictionary` with the values wrapped as `Weak<Value>`. Its contents can be accessed either via a `subscript` getter or the `contents` property, which returns a `Dictionary` with those key-value-pairs whose value is currently non-nil. This enables use of Swift-implemented methods on the `Dictionary` type. | ||
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| Apart from everything implemented by the protocols it conforms to, `WeakDictionary` offers: | ||
| - a subscript to `get` and `set` values for a key | ||
| - a method to clean out all those `Weak<Element>` instances internally stored that wrap a value already being `nil` | ||
| - the `contents` property | ||
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| ## Use | ||
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| You can create a `WeakDictionary` using a dictionary literal: | ||
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| ```swift | ||
| var weakDictionary: WeakDictionary<String: UIView> = ["test1": UIView(), "test2": UIView()] | ||
| ``` | ||
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| To set a value for a key, use a `subscript` setter: | ||
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| ```swift | ||
| let myView = UIView() | ||
| weakDictionary["test3"] = myView | ||
| ``` | ||
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| To remove a value for a key, use a `subscript` setter with the value being `nil`: | ||
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| ```swift | ||
| weakDictionary["test3"] = nil | ||
| ``` | ||
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| If you don't call the `subscript` setter, that auto-performs a clean, it may be suitable to call it manually from time to time for a large `WeakDictionary`. | ||
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| ```swift | ||
| weakDictionary.clean() // Cleans out internal Weak<Element> instances whose contained value is nil | ||
| ``` | ||
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| To get the value for a key, you can use a `subscript` getter: | ||
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| ```swift | ||
| weakDictionary["test3"] // Returns nil for this configuration | ||
| ``` | ||
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| To access the `WeakDictionary`'s contents apart from the simple getter, you should use `contents`, which returns a dicionary of those key-value-pairs where the value isn't `nil`. At this point you can use interfaces provided by the `Dictionary` implementation of Swift. | ||
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| ```swift | ||
| print(weakDictionary.keys) | ||
| print(weakDictionary.values) | ||
| print(weakDictionary.count) | ||
| ``` |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,57 @@ | ||
| // | ||
| // WeakDictionary.swift | ||
| // SwiftCollections | ||
| // | ||
| // Created by Frederick Pietschmann on 12.03.18. | ||
| // Copyright © 2018 Piknotech. All rights reserved. | ||
| // | ||
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| import Foundation | ||
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| struct WeakDictionary<Key: Hashable, Value: Hashable> where Value: AnyObject { | ||
| // MARK: - Properties | ||
| var contents: [Key: Value] { | ||
| return wrappedContents.filter { $0.value.value != nil }.mapValues { $0.value! } | ||
| } | ||
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| private var wrappedContents = [Key: Weak<Value>]() | ||
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| // MARK: - Initializers | ||
| init() { } | ||
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| init(_ dictionary: [Key: Value]) { | ||
| dictionary.forEach { key, value in | ||
| wrappedContents[key] = Weak(value) | ||
| } | ||
| } | ||
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| // MARK: - Subscripts | ||
| subscript(key: Key) -> Value? { | ||
| get { | ||
| return wrappedContents[key]?.value | ||
| } | ||
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| set(newValue) { | ||
| clean() | ||
| wrappedContents[key] = newValue.map(Weak.init) | ||
| } | ||
| } | ||
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| mutating func clean() { | ||
| wrappedContents = wrappedContents.filter { $0.value.value != nil } | ||
| } | ||
| } | ||
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| // MARK: - CustomStringConvertible | ||
| extension WeakDictionary: CustomStringConvertible { | ||
| var description: String { | ||
| return "WeakDictionary<\(String(describing: contents))>" | ||
| } | ||
| } | ||
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| // MARK: - ExpressibleByDictionaryLiteral | ||
| extension WeakDictionary: ExpressibleByDictionaryLiteral { | ||
| init(dictionaryLiteral elements: (Key, Value)...) { | ||
| self.init() // TODO | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,62 @@ | ||
| // | ||
| // WeakDictionaryTests.swift | ||
| // SwiftCollections | ||
| // | ||
| // Created by Frederick Pietschmann on 16.04.18. | ||
| // Copyright © 2018 Piknotech. All rights reserved. | ||
| // | ||
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| import Foundation | ||
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| @testable import SwiftCollections | ||
| import XCTest | ||
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| class WeakDictionaryTests: XCTestCase { | ||
| // MARK: - Subtypes | ||
| class SampleObject: Hashable { | ||
| var hashValue: Int | ||
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| init(_ hashValue: Int) { | ||
| self.hashValue = hashValue | ||
| } | ||
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| static func == (lhs: SampleObject, rhs: SampleObject) -> Bool { | ||
| return lhs.hashValue == rhs.hashValue | ||
| } | ||
| } | ||
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| // MARK: - Properties | ||
| private let dictionarySize = 3 | ||
| private lazy var dictionary: [Int: SampleObject]? = { | ||
| let tuples = (0..<dictionarySize).map { (key: $0, value: SampleObject($0)) } | ||
| return Dictionary(tuples) { _, _ in fatalError() } | ||
| }() | ||
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| // MARK: - Methods | ||
| func testCount() { | ||
| let weakDictionary = WeakDictionary(dictionary!) | ||
| XCTAssertEqual(weakDictionary.contents.count, dictionary!.count) | ||
| } | ||
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| func testAddingAndRemoving() { | ||
| var weakDictionary = WeakDictionary(dictionary!) | ||
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| // Test adding | ||
| let sampleKey = dictionary!.count | ||
| let sampleValue = dictionary!.first!.value | ||
| weakDictionary[sampleKey] = sampleValue | ||
| XCTAssertEqual(weakDictionary[sampleKey], sampleValue) | ||
| XCTAssertEqual(weakDictionary.contents.values.count, dictionary!.count + 1) | ||
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| // Test removing | ||
| weakDictionary[sampleKey] = nil | ||
| XCTAssertEqual(weakDictionary[sampleKey], nil) | ||
| XCTAssertEqual(weakDictionary.contents.values.count, dictionary!.count) | ||
| } | ||
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| func testCleaning() { | ||
| let weakDictionary = WeakDictionary(dictionary!) | ||
| dictionary = nil | ||
| XCTAssertEqual(weakDictionary.contents.isEmpty, true) | ||
| } | ||
| } |