Merge pull request #18 from ReactiveCocoa/anders/xcode-12

Fix Xcode 12 compiler segfault in EnvironmentLoop.

Author: andersio

Loop/Public/SwiftUI/EnvironmentLoop.swift

@@ -7,8 +7,10 @@ import ReactiveSwift
 @available(macOS 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
 @propertyWrapper
 public struct EnvironmentLoop<State, Event>: DynamicProperty {
-    @Environment(\.loops[LoopType(Loop<State, Event>.self)])
-    var erasedLoop: AnyObject?
+    static var loopType: LoopType { LoopType(Loop<State, Event>.self) }
+
+    @Environment(\.loops)
+    var erasedLoops: [LoopType: AnyObject]
 
     @ObservedObject
     private var subscription: SwiftUIHotSwappableSubscription<State, Event>
@@ -19,7 +21,7 @@ public struct EnvironmentLoop<State, Event>: DynamicProperty {
     }
 
     public var projectedValue: LoopBinding<State, Event> {
-        guard let loop = erasedLoop as! Loop<State, Event>? else {
+        guard let loop = erasedLoops[Self.loopType] as! Loop<State, Event>? else {
             fatalError("Scoped bindings can only be created inside the view body.")
         }
 
@@ -34,7 +36,7 @@ public struct EnvironmentLoop<State, Event>: DynamicProperty {
     }
 
     public mutating func update() {
-        guard let loop = erasedLoop as! Loop<State, Event>? else {
+        guard let loop = erasedLoops[Self.loopType] as! Loop<State, Event>? else {
             fatalError("Expect parent view to inject a `Loop<\(State.self), \(Event.self)>` through `View.environmentLoop(_:)`. Found none.")
         }