refactor and cleanup [skip ci]

submodules/Postbox/Sources/MessageHistoryHolesView.swift

@@ -0,0 +1,37 @@
+import Foundation
+
+public struct MessageHistoryHolesViewEntry: Equatable, Hashable {
+    public let hole: MessageHistoryViewHole
+    public let direction: MessageHistoryViewRelativeHoleDirection
+    public let space: MessageHistoryHoleSpace
+    
+    public init(hole: MessageHistoryViewHole, direction: MessageHistoryViewRelativeHoleDirection, space: MessageHistoryHoleSpace) {
+        self.hole = hole
+        self.direction = direction
+        self.space = space
+    }
+}
+
+final class MutableMessageHistoryHolesView {
+    fileprivate var entries = Set<MessageHistoryHolesViewEntry>()
+    
+    init() {
+    }
+    
+    func update(_ holes: Set<MessageHistoryHolesViewEntry>) -> Bool {
+        if self.entries != holes {
+            self.entries = holes
+            return true
+        } else {
+            return false
+        }
+    }
+}
+
+public final class MessageHistoryHolesView {
+    public let entries: Set<MessageHistoryHolesViewEntry>
+    
+    init(_ mutableView: MutableMessageHistoryHolesView) {
+        self.entries = mutableView.entries
+    }
+}