0001    //
0002    //  PromiseType.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    /// A promise models writing the result of some asynchronous operation.
0010    ///
0011    /// Promises should generally only be determined, or "filled", once. This allows
0012    /// an implementing type to clear a queue of subscribers, for instance, and
0013    /// provides consistent sharing of the determined value.
0014    ///
0015    /// An implementing type should discourage race conditions around filling.
0016    /// However, certain use cases inherently race (such as cancellation), and any
0017    /// attempts to check for programmer error should be active by default.
0018    ///
0019    public protocol PromiseType
Deferred.swift:41
public struct Deferred<Value>: FutureType, PromiseType {
PromiseType.swift:39
public extension PromiseType { {
0020        /// A type that represents the result of some asynchronous operation.
0021        typealias Value
PromiseType.swift:36
    func fill(value: Value) -> Bool
PromiseType.swift:59
    func fill(value: Value, assertIfFilled: Bool, file: StaticString = __FILE__, line: UInt = __LINE__) {
0022        
0023        /// Create the promise in a default, unfilled state
0024        init()
0025    
0026        /// Check whether or not the receiver is filled.
0027        var isFilled: Bool { get }
0028    
0029        /// Determines the deferred value with a given result.
0030        ///
0031        /// Filling a deferred value should usually be attempted only once. An
0032        /// implementing type may choose to enforce this.
0033        ///
0034        /// - parameter value: A resolved value for the instance.
0035        /// - returns: Whether the promise was fulfilled with `value`.
0036        func fill
PromiseType.swift:60
        if !fill(value) && assertIfFilled {(value: Value) -> Bool
0037    }
0038    
0039    public extension PromiseType {
0040        /// Determines the deferred value with a given result.
0041        ///
0042        /// Filling a deferred value should usually be attempted only once. An
0043        /// implementing type may choose to enforce this by default. If an
0044        /// implementing type requires multiple potential fillers to race, the
0045        /// precondition may be disabled.
0046        ///
0047        /// * In playgrounds and unoptimized builds (the default for a "Debug"
0048        ///   configuration), program execution should be stopped at the caller in
0049        ///   a debuggable state.
0050        ///
0051        /// * In -O builds (the default for a "Release" configuration), program
0052        ///   execution should stop.
0053        ///
0054        /// * In -Ounchecked builds, the programming error should be assumed to not
0055        ///   exist.
0056        ///
0057        /// - parameter value: A resolved value for the instance.
0058        /// - parameter assertIfFilled: If `false`, race checking is disabled.
0059        func fill(value: Value, assertIfFilled: Bool, file: StaticString = __FILE__, line: UInt = __LINE__) {
0060            if !fill(value) && assertIfFilled {
0061                assertionFailure("Cannot fill an already-filled \(self.dynamicType)", file: file, line: line)
0062            }
0063        }
0064    }
0065