Merge pull request ReactiveCocoa#2601 from Adlai-Holler/UpdateAtomic

Add Support for Rethrowing in Atomic Closure Methods

ReactiveCocoa/Swift/Atomic.swift

@@ -51,24 +51,23 @@ public final class Atomic<Value> {
 	/// Atomically modifies the variable.
 	///
 	/// Returns the old value.
-	public func modify(@noescape action: Value -> Value) -> Value {
+	public func modify(@noescape action: (Value) throws -> Value) rethrows -> Value {
 		lock()
+		defer { unlock() }
+
 		let oldValue = _value
-		_value = action(_value)
-		unlock()
-
+		_value = try action(_value)
 		return oldValue
 	}
 
 	/// Atomically performs an arbitrary action using the current value of the
 	/// variable.
 	///
 	/// Returns the result of the action.
-	public func withValue<U>(@noescape action: Value -> U) -> U {
+	public func withValue<Result>(@noescape action: (Value) throws -> Result) rethrows -> Result {
 		lock()
-		let result = action(_value)
-		unlock()
-
-		return result
+		defer { unlock() }
+
+		return try action(_value)
 	}
 }