Weakify progressValue if possible, for less memory footprint.

Author: inamiy

SwiftTask/SwiftTask.swift

@@ -74,7 +74,7 @@ public class Task<Progress, Value, Error>: Printable
 
     public var state: TaskState { return self._machine.state }
 
-    /// progress value
+    /// progress value (NOTE: always nil when `weakified = true`)
     public var progress: Progress? { return self._machine.progress }
 
     /// fulfilled value
@@ -118,7 +118,7 @@ public class Task<Progress, Value, Error>: Printable
     {
         self._weakified = weakified
         self._paused = paused
-        self._machine = _Machine(paused: paused)
+        self._machine = _Machine(weakified: weakified, paused: paused)
 
         let _initClosure: _InitClosure = { _, progress, fulfill, _reject, configure in
             // NOTE: don't expose rejectHandler with ErrorInfo (isCancelled) for public init
@@ -192,7 +192,7 @@ public class Task<Progress, Value, Error>: Printable
     {
         self._weakified = weakified
         self._paused = paused
-        self._machine = _Machine(paused: paused)
+        self._machine = _Machine(weakified: weakified, paused: paused)
 
         self.setup(weakified, paused: paused, _initClosure)
     }
@@ -325,6 +325,8 @@ public class Task<Progress, Value, Error>: Printable
     ///
     /// - e.g. task.progress { oldProgress, newProgress in ... }
     ///
+    /// NOTE: `oldProgress` is always nil when `weakified = true`
+    ///
     public func progress(progressClosure: ProgressTuple -> Void) -> Task
     {
         self._machine.progressTupleHandlers.append(progressClosure)

SwiftTask/_StateMachine.swift

@@ -14,6 +14,7 @@ internal class _StateMachine<Progress, Value, Error>
 {
     internal typealias ErrorInfo = Task<Progress, Value, Error>.ErrorInfo
 
+    internal let weakified: Bool
     internal var state: TaskState
 
     internal var progress: Progress?
@@ -25,15 +26,19 @@ internal class _StateMachine<Progress, Value, Error>
 
     internal let configuration = TaskConfiguration()
 
-    internal init(paused: Bool)
+    internal init(weakified: Bool, paused: Bool)
     {
+        self.weakified = weakified
         self.state = paused ? .Paused : .Running
     }
 
     internal func handleProgress(progress: Progress)
     {
         let oldProgress = self.progress
-        self.progress = progress
+        
+        if !self.weakified {
+            self.progress = progress
+        }
 
         if self.state == .Running {
             for handler in self.progressTupleHandlers {