d

src/Cord.Button.swift

@@ -0,0 +1,16 @@
+import Combine
+
+extension Cord {
+  final class Button: ObservableObject {
+    let press = PassthroughSubject<Void, Never>()
+    var subscriptions = [AnyCancellable]()
+   
+    init(_ key: String) {
+      Bus.send(
+        key,
+        press.eraseToAnyPublisher(),
+        sub: &subscriptions
+      )
+    }
+  }
+}

src/Cord.ReadOnly.swift

@@ -0,0 +1,20 @@
+import Combine
+
+extension Cord {
+  final class ReadOnly<T>: ObservableObject {
+    @Published var value: T
+    var subscriptions = [AnyCancellable]()
+   
+    init(
+      _ key: String,
+      _ defaultValue: T
+    ) {
+      value = defaultValue
+      Bus.receive(
+        [key],
+        { [weak self] (_, v: T) in self?.value = v },
+        sub: &subscriptions
+      )
+    }
+  }
+}

src/Cord.TextField.swift

@@ -12,7 +12,7 @@ extension Cord {
     ) {
       Bus.send(
         textUI,
-        $value.compactMap(onlyUIText).eraseToAnyPublisher(),
+        $value.removeDuplicates().compactMap(onlyUIText).eraseToAnyPublisher(),
         sub: &subscriptions
       )
    

src/MeetupId.swift

@@ -7,6 +7,10 @@ enum MeetupId {
     case meetupIdTextUI
   }
 
+  static func onlyAllowJoin(_ s: String) -> Bool? {
+    s.hasPrefix("123")
+  }
+
   static func onlyFormat(_ s: String) -> String? {
     let digits = s.components(separatedBy: NSCharacterSet.decimalDigits.inverted).reduce("") { $0 + $1 }
     var r = ""

src/V.swift

@@ -1,27 +1,32 @@
 import SwiftUI
 
 struct V: View {
-  @StateObject var tf = Cord.TextField("text.app", "text.ui")
-  @StateObject var vm = VM()
+  @StateObject var isJoinAvailable = Cord.ReadOnly("joinAvailable", false)
+  @StateObject var join = Cord.Button("join")
+  @StateObject var textF = Cord.TextField("text.app", "text.ui")
+  let test = Bus.Processor("text.ui", "joinAvailable", MeetupId.onlyAllowJoin)
   
   var body: some View {
     VStack {
       HStack {
         Text("Check text field:")
-        Text("'\(tf.value)'")
+        Text("'\(textF.value)'")
           .fontWeight(.bold)
       }
 
-      TextField("Binding-3", value: $tf.value, formatter: TextFieldValueOwner())
+      TextField("Binding-3", value: $textF.value, formatter: TextFieldValueOwner())
         .padding(8)
         .border(Color.blue, width: 2)
 
-      Button(action: vm.join.send) {
+      Button(action: join.press.send) {
         Text("Join")
           .padding(8)
-          .border(vm.isJoinAvailable ? Color.green : Color.red, width: 4)
+          .border(
+            isJoinAvailable.value ? Color.green : Color.gray,
+            width: isJoinAvailable.value ? 4 : 1
+          )
       }
-
+      .disabled(!isJoinAvailable.value)
     }
     .frame(width: 320)
     .padding()

src/VM.swift

@@ -10,8 +10,7 @@ final class VM: ObservableObject {
     MeetupId.onlyFormat
   )
      */
-  var isJoinAvailable = true
-  let join = PassthroughSubject<Void, Never>()
+  var isJoinAvailable = false
   var subscriptions = [AnyCancellable]()
 
   init() {