refactor and cleanup [skip ci]

submodules/Postbox/Sources/PostboxView.swift

@@ -0,0 +1,43 @@
+import Foundation
+
+public protocol PostboxView {
+}
+
+protocol MutablePostboxView {
+    func replay(postbox: Postbox, transaction: PostboxTransaction) -> Bool
+    func immutableView() -> PostboxView
+}
+
+final class CombinedMutableView {
+    private let views: [PostboxViewKey: MutablePostboxView]
+    
+    init(views: [PostboxViewKey: MutablePostboxView]) {
+        self.views = views
+    }
+    
+    func replay(postbox: Postbox, transaction: PostboxTransaction) -> Bool {
+        var updated = false
+        for (_, view) in self.views {
+            if view.replay(postbox: postbox, transaction: transaction) {
+                updated = true
+            }
+        }
+        return updated
+    }
+    
+    func immutableView() -> CombinedView {
+        var result: [PostboxViewKey: PostboxView] = [:]
+        for (key, view) in self.views {
+            result[key] = view.immutableView()
+        }
+        return CombinedView(views: result)
+    }
+}
+
+public final class CombinedView {
+    public let views: [PostboxViewKey: PostboxView]
+    
+    init(views: [PostboxViewKey: PostboxView]) {
+        self.views = views
+    }
+}