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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift open source project
//
// Copyright (c) 2025 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
import Foundation
/// Generic protocol representing operations common to dictionaries, caches, and other key-value stores.
public protocol KeyValueStorage<Key, Value> {
associatedtype Key
associatedtype Value
func getOrInsert(_ key: Key, _ body: () throws -> Value) rethrows -> Value
}
extension KeyValueStorage {
public func getOrInsert<Wrapped>(_ key: Key, body: () throws -> Wrapped) rethrows -> Wrapped where Value == Lazy<Wrapped> {
return try getOrInsert(key, isValid: { _ in true }, body: body)
}
/// Gets or inserts a value into the key-value store using `Lazy` as its value type.
///
/// This is used as a convenience wrapper which effectively implements a uses two-level lock: one to protect the key-value store itself, and one lock per value, so that values can be computed in parallel while maintaining the guarantee that `body` is called only once per key.
///
/// - parameter key: The key used to identify the value in the key-value store.
/// - parameter isValid: A closure used to indicate whether the existing stored value for `key` is still valid. Return `false` to discard the currently cached value and call `body` to compute a new value.
/// - parameter body: A closure used to compute the value for `key`. Will be called at most once per key in case of race conditions.
public func getOrInsert<Wrapped>(_ key: Key, isValid: (Wrapped) throws -> Bool, body: () throws -> Wrapped) rethrows -> Wrapped where Value == Lazy<Wrapped> {
return try getOrInsert(key) { .init() }.getValue(body, isValid: isValid)
}
}
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