Revision control
Copy as Markdown
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
import Foundation
/**
* A list that weakly holds references to its items.
* Note that while the references themselves are cleared, their wrapper objects
* are not (though they are reused). Also note that since slots are reused,
* order is not preserved.
*
* This class crashes at runtime with EXC_BAD_ACCESS if a protocol is given as
* the type T. Make sure to use a class type.
*/
open class WeakList<T: AnyObject>: Sequence {
private var items = [WeakRef<T>]()
public init() {}
/**
* Adds an item to the list.
* Note that every insertion iterates through the list to find any "holes" (items that have
* been deallocated) to reuse them, so this class may not be appropriate in situations where
* insertion is frequent.
*/
open func insert(_ item: T, at: Int? = nil) {
// Reuse any existing slots that have been deallocated.
for wrapper in items where wrapper.value == nil {
wrapper.value = item
return
}
if let at = at, 0...items.endIndex ~= at {
items.insert(WeakRef(item), at: at)
} else {
items.append(WeakRef(item))
}
}
open var count: Int {
return items.count
}
open var isEmpty: Bool {
return items.isEmpty
}
open func removeAll() {
items.removeAll()
}
@discardableResult
open func remove(_ item: T) -> Int? {
guard let index = self.index(of: item) else { return nil }
items.remove(at: index)
return index
}
open func at(_ index: Int) -> T? {
return items[safe: index]?.value
}
open func index(of item: T) -> Int? {
return items.firstIndex { $0.value === item }
}
open func firstIndexDel(where predicate: (WeakRef<T>) -> Bool) -> Int? {
return items.firstIndex(where: predicate)
}
open func makeIterator() -> AnyIterator<T> {
var index = 0
return AnyIterator {
if index >= self.items.count {
return nil
}
for i in index..<self.items.count {
if let value = self.items[i].value {
index = i + 1
return value
}
}
index = self.items.count
return nil
}
}
}
open class WeakRef<T: AnyObject> {
public weak var value: T?
public init(_ value: T) {
self.value = value
}
}