0001    //
0002    //  ExistentialFuture.swift
0003    //  Deferred
0004    //
0005    //  Created by Zachary Waldowski on 8/29/15.
0006    //  Copyright © 2014-2015 Big Nerd Ranch. Licensed under MIT.
0007    //
0008    
0009    import Dispatch
0010    
0011    /*
0012    The types in this file provide an implementation of type erasure for `FutureType`.
0013    The techniques were derived from experimenting with `AnySequence` and `Mirror`
0014    in a playground, the following post, and the Swift standard library:
0015     - https://realm.io/news/type-erased-wrappers-in-swift/
0016     - https://github.com/apple/swift/blob/master/stdlib/public/core/ExistentialCollection.swift.gyb
0017    */
0018    
0019    // Abstract class that fake-conforms to `FutureType` for use by `Future`.
0020    private class FutureBase
ExistentialFuture.swift:31
private final class ForwardingFuture<Future: FutureType>: FutureBase<Future.Value> {
ExistentialFuture.swift:47
private final class FilledFuture<Value>: FutureBase<Value> {
ExistentialFuture.swift:77
    private let box: FutureBase<Value>
<Value
ExistentialFuture.swift:21
    func upon(queue: dispatch_queue_t, body: Value -> ()) {
ExistentialFuture.swift:25
    func wait(time: Timeout) -> Value? {
>: FutureType {
0021        func upon
ExistentialFuture.swift:99
        return box.upon(queue, body: body)
(queue: dispatch_queue_t, body: Value -> ()) {
0022            fatalError()
0023        }
0024    
0025        func wait
ExistentialFuture.swift:107
        return box.wait(time)
(time: Timeout) -> Value? {
0026            fatalError()
0027        }
0028    }
0029    
0030    // Concrete future wrapper given an instance of a `FutureType`.
0031    private final class ForwardingFuture
ExistentialFuture.swift:81
        self.box = ForwardingFuture(base: base)
<Future
ExistentialFuture.swift:31
private final class ForwardingFuture<Future: FutureType>: FutureBase<Future.Value> {
ExistentialFuture.swift:32
    let base: Future
ExistentialFuture.swift:33
    init(base: Future) {
ExistentialFuture.swift:37
    override func upon(queue: dispatch_queue_t, body: Future.Value -> ()) {
ExistentialFuture.swift:41
    override func wait(time: Timeout) -> Future.Value? {
: FutureType>: FutureBase<Future.Value> {
0032        let base
ExistentialFuture.swift:34
        self.base = base
ExistentialFuture.swift:38
        return base.upon(queue, body: body)
ExistentialFuture.swift:42
        return base.wait(time)
: Future
0033        init
ExistentialFuture.swift:81
        self.box = ForwardingFuture(base: base)
(base: Future) {
0034            self.base = base
0035        }
0036    
0037        override func upon(queue: dispatch_queue_t, body: Future.Value -> ()) {
0038            return base.upon(queue, body: body)
0039        }
0040    
0041        override func wait(time: Timeout) -> Future.Value? {
0042            return base.wait(time)
0043        }
0044    }
0045    
0046    // Concrete future wrapper for an always-filled future.
0047    private final class FilledFuture
ExistentialFuture.swift:86
        self.box = FilledFuture(value: value)
<Value
ExistentialFuture.swift:47
private final class FilledFuture<Value>: FutureBase<Value> {
ExistentialFuture.swift:48
    let value: Value
ExistentialFuture.swift:49
    init(value: Value) {
ExistentialFuture.swift:53
    override func upon(queue: dispatch_queue_t, body: Value -> ()) {
ExistentialFuture.swift:59
    override func wait(time: Timeout) -> Value? {
>: FutureBase<Value> {
0048        let value
ExistentialFuture.swift:50
        self.value = value
ExistentialFuture.swift:54
        dispatch_async(queue) { [value] in
ExistentialFuture.swift:60
        return value
: Value
0049        init
ExistentialFuture.swift:86
        self.box = FilledFuture(value: value)
(value: Value) {
0050            self.value = value
0051        }
0052    
0053        override func upon(queue: dispatch_queue_t, body: Value -> ()) {
0054            dispatch_async(queue) { [value] in
0055                body(value)
0056            }
0057        }
0058    
0059        override func wait(time: Timeout) -> Value? {
0060            return value
0061        }
0062    }
0063    
0064    /// A type-erased wrapper over any future.
0065    ///
0066    /// Forwards operations to an arbitrary underlying future having the same
0067    /// `Value` type, hiding the specifics of the underlying `FutureType`.
0068    ///
0069    /// Authors can use this type to:
0070    ///
0071    /// - Prevent clients from coupling to the specific kind of `FutureType` your
0072    ///   implementation is currently using.
0073    /// - Publicly expose only the `FutureType` aspect of a deferred value,
0074    ///   ensuring that only your implementation can fill the deferred value
0075    ///   using the `PromiseType` aspect.
0076    public struct Future
ExistentialFuture.swift:90
    public init(_ other: Future<Value>) {
FutureCollections.swift:23
        return Future(combined)
FutureCollections.swift:16
    var earliestFilled: Future<Generator.Element.Value> {
FutureCollections.swift:34
            return Future(value: [])
FutureCollections.swift:54
        return Future(combined)
FutureCollections.swift:32
    var joinedValues: Future<[Generator.Element.Value]> {
FutureType.swift:127
    func flatMap<NewFuture: FutureType>(upon queue: dispatch_queue_t = genericQueue, _ transform: Value -> NewFuture) -> Future<NewFuture.Value> {
FutureType.swift:134
        return Future(d)
FutureType.swift:147
    func map<NewValue>(upon queue: dispatch_queue_t = genericQueue, _ transform: Value -> NewValue) -> Future<NewValue> {
FutureType.swift:152
        return Future(d)
FutureType.swift:163
    func and<OtherFuture: FutureType>(other: OtherFuture) -> Future<(Value, OtherFuture.Value)> {
FutureType.swift:164
        return Future(flatMap { t in other.map { u in (t, u) } })
FutureType.swift:174
    func and<Other1: FutureType, Other2: FutureType>(one: Other1, _ two: Other2) -> Future<(Value, Other1.Value, Other2.Value)> {
FutureType.swift:175
        return Future(flatMap { t in
FutureType.swift:190
    func and<Other1: FutureType, Other2: FutureType, Other3: FutureType>(one: Other1, _ two: Other2, _ three: Other3) -> Future<(Value, Other1.Value, Other2.Value, Other3.Value)> {
FutureType.swift:191
        return Future(flatMap { t in
<Value
ExistentialFuture.swift:77
    private let box: FutureBase<Value>
ExistentialFuture.swift:80
    public init<Future: FutureType where Future.Value == Value>(_ base: Future) {
ExistentialFuture.swift:85
    public init(value: Value) {
ExistentialFuture.swift:90
    public init(_ other: Future<Value>) {
ExistentialFuture.swift:98
    public func upon(queue: dispatch_queue_t, body: Value -> ()) {
ExistentialFuture.swift:106
    public func wait(time: Timeout) -> Value? {
>: FutureType {
0077        private let box
ExistentialFuture.swift:81
        self.box = ForwardingFuture(base: base)
ExistentialFuture.swift:86
        self.box = FilledFuture(value: value)
ExistentialFuture.swift:91
        self.box = other.box
ExistentialFuture.swift:91
        self.box = other.box
ExistentialFuture.swift:99
        return box.upon(queue, body: body)
ExistentialFuture.swift:107
        return box.wait(time)
: FutureBase<Value>
0078    
0079        /// Create a future whose `upon(_:function:)` method forwards to `base`.
0080        public init
FutureCollections.swift:23
        return Future(combined)
FutureCollections.swift:54
        return Future(combined)
FutureType.swift:134
        return Future(d)
FutureType.swift:152
        return Future(d)
<Future: FutureType where Future.Value == Value>(_ base: Future) {
0081            self.box = ForwardingFuture(base: base)
0082        }
0083    
0084        /// Wrap and forward future as if it were always filled with `value`.
0085        public init
FutureCollections.swift:34
            return Future(value: [])
(value: Value) {
0086            self.box = FilledFuture(value: value)
0087        }
0088        
0089        /// Create a future having the same underlying future as `other`.
0090        public init
FutureType.swift:164
        return Future(flatMap { t in other.map { u in (t, u) } })
FutureType.swift:175
        return Future(flatMap { t in
FutureType.swift:191
        return Future(flatMap { t in
(_ other: Future<Value>) {
0091            self.box = other.box
0092        }
0093    
0094        /// Call some function once the underlying future's value is determined.
0095        ///
0096        /// - parameter queue: A dispatch queue for executing the given function on.
0097        /// - parameter function: A function that uses the determined value.
0098        public func upon(queue: dispatch_queue_t, body: Value -> ()) {
0099            return box.upon(queue, body: body)
0100        }
0101    
0102        /// Waits synchronously for the underlying future to become determined.
0103        ///
0104        /// - parameter time: A length of time to wait for the value to be determined.
0105        /// - returns: The determined value, if filled within the timeout, or `nil`.
0106        public func wait(time: Timeout) -> Value? {
0107            return box.wait(time)
0108        }
0109    }
0110