Add @EnvironmentObject

Sources/TokamakCore/Environment/Environment.swift

@@ -12,6 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+/// A protocol that allows the conforming type to access values from the `EnvironmentValues`.
+/// (e.g. `Environment` and `EnvironmentObject`)
+///
+/// `EnvironmentValues` are injected in 2 places:
+/// 1. `View.makeMountedView`
+/// 2. `MountedHostView.update` when reconciling
+///
 protocol EnvironmentReader {
   mutating func setContent(from values: EnvironmentValues)
 }
@@ -22,7 +29,7 @@ protocol EnvironmentReader {
     case value(Value)
   }
 
-  var content: Environment<Value>.Content
+  var content: Content
   let keyPath: KeyPath<EnvironmentValues, Value>
   public init(_ keyPath: KeyPath<EnvironmentValues, Value>) {
     content = .keyPath(keyPath)

Sources/TokamakCore/Environment/EnvironmentObject.swift

@@ -0,0 +1,76 @@
+// Copyright 2020 Tokamak contributors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+//  Created by Carson Katri on 7/7/20.
+//
+
+import OpenCombine
+
+@propertyWrapper public struct EnvironmentObject<ObjectType>: ObservedProperty,
+  EnvironmentReader
+  where ObjectType: ObservableObject {
+  @dynamicMemberLookup public struct Wrapper {
+    internal let root: ObjectType
+    public subscript<Subject>(
+      dynamicMember keyPath: ReferenceWritableKeyPath<ObjectType, Subject>
+    ) -> Binding<Subject> {
+      .init(
+        get: {
+          self.root[keyPath: keyPath]
+        }, set: {
+          self.root[keyPath: keyPath] = $0
+        }
+      )
+    }
+  }
+
+  var _store: ObjectType?
+  var _seed: Int = 0
+
+  mutating func setContent(from values: EnvironmentValues) {
+    _store = values[ObjectIdentifier(ObjectType.self)]
+  }
+
+  public var wrappedValue: ObjectType {
+    guard let store = _store else { error() }
+    return store
+  }
+
+  public var projectedValue: Wrapper {
+    guard let store = _store else { error() }
+    return Wrapper(root: store)
+  }
+
+  var objectWillChange: AnyPublisher<(), Never> {
+    wrappedValue.objectWillChange.map { _ in }.eraseToAnyPublisher()
+  }
+
+  func error() -> Never {
+    fatalError("No ObservableObject found for type \(ObjectType.self)")
+  }
+
+  public init() {}
+}
+
+extension ObservableObject {
+  static var environmentStore: WritableKeyPath<EnvironmentValues, Self?> {
+    \.[ObjectIdentifier(self)]
+  }
+}
+
+extension View {
+  public func environmentObject<B>(_ bindable: B) -> some View where B: ObservableObject {
+    environment(B.environmentStore, bindable)
+  }
+}

Sources/TokamakCore/Environment/EnvironmentValues.swift

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+import OpenCombine
+
 public struct EnvironmentValues: CustomStringConvertible {
   public var description: String {
     String(describing: values)
@@ -32,4 +34,13 @@ public struct EnvironmentValues: CustomStringConvertible {
       values[ObjectIdentifier(key)] = newValue
     }
   }
+
+  subscript<B>(bindable: ObjectIdentifier) -> B? where B: ObservableObject {
+    get {
+      values[bindable] as? B
+    }
+    set {
+      values[bindable] = newValue
+    }
+  }
 }

Sources/TokamakCore/MountedViews/MountedHostView.swift

@@ -15,6 +15,8 @@
 //  Created by Max Desiatov on 03/12/2018.
 //
 
+import Runtime
+
 /* A representation of a `View`, which has a `body` of type `Never`, stored in the tree of mounted
  views by `StackReconciler`.
  */
@@ -103,6 +105,17 @@ public final class MountedHostView<R: Renderer>: MountedView<R> {
         let newChild: MountedView<R>
         if firstChild.typeConstructorName == mountedChildren[0].view.typeConstructorName {
           child.view = firstChild
+          // Inject Environment
+          // swiftlint:disable force_try
+          let viewInfo = try! typeInfo(of: child.view.type)
+          for prop in viewInfo.properties.filter({ $0.type is EnvironmentReader.Type }) {
+            // swiftlint:disable force_cast
+            var wrapper = try! prop.get(from: child.view.view) as! EnvironmentReader
+            wrapper.setContent(from: environmentValues)
+            try! prop.set(value: wrapper, on: &child.view.view)
+            // swiftlint:enable force_cast
+          }
+          // swiftlint:enable force_try
           child.update(with: reconciler)
           newChild = child
         } else {

Sources/TokamakCore/MountedViews/MountedView.swift

@@ -44,36 +44,37 @@ extension View {
     // Find Environment changes
     var modifiedEnv = environmentValues
     var injectableView = self
-    if let any = injectableView as? AnyView {
-      // swiftlint:disable force_try
-      // Extract the view from the AnyView for modification
-      var extractedView = any.view
-      let viewInfo = try! typeInfo(of: any.type)
-      if viewInfo
-        .genericTypes
-        .filter({ $0 is EnvironmentModifier.Type }).count > 0 {
-        // Apply Environment changes:
-        if let modifier = try? viewInfo
-          .property(named: "modifier")
-          .get(from: any.view) as? EnvironmentModifier {
-          modifier.modifyEnvironment(&modifiedEnv)
-        }
+    let any = (injectableView as? AnyView) ?? AnyView(injectableView)
+    // swiftlint:disable force_try
+    // Extract the view from the AnyView for modification
+    var extractedView = any.view
+    let viewInfo = try! typeInfo(of: any.type)
+    if viewInfo
+      .genericTypes
+      .filter({ $0 is EnvironmentModifier.Type }).count > 0 {
+      // Apply Environment changes:
+      if let modifier = try? viewInfo
+        .property(named: "modifier")
+        .get(from: any.view) as? EnvironmentModifier {
+        modifier.modifyEnvironment(&modifiedEnv)
       }
-      // Inject @Environment values
-      // In the future we can also inject @EnvironmentObject values
-      for prop in viewInfo.properties.filter({ $0.type is EnvironmentReader.Type }) {
-        // swiftlint:disable force_cast
-        var wrapper = try! prop.get(from: any.view) as! EnvironmentReader
-        wrapper.setContent(from: modifiedEnv)
-        try! prop.set(value: wrapper, on: &extractedView)
-        // swiftlint:enable force_cast
-      }
-      // Set the extractedView back on the AnyView after modification
-      let anyViewInfo = try! typeInfo(of: AnyView.self)
-      try! anyViewInfo.property(named: "view").set(value: extractedView, on: &injectableView)
-      // swiftlint:enable force_try
     }
 
+    // Inject @Environment values
+    for prop in viewInfo.properties.filter({ $0.type is EnvironmentReader.Type }) {
+      // swiftlint:disable force_cast
+      var wrapper = try! prop.get(from: any.view) as! EnvironmentReader
+      wrapper.setContent(from: modifiedEnv)
+      try! prop.set(value: wrapper, on: &extractedView)
+      // swiftlint:enable force_cast
+    }
+
+    // Set the extractedView back on the AnyView after modification
+    let anyViewInfo = try! typeInfo(of: AnyView.self)
+    try! anyViewInfo.property(named: "view").set(value: extractedView, on: &injectableView)
+    // swiftlint:enable force_try
+
+    // Make MountedView
     let anyView = injectableView as? AnyView ?? AnyView(injectableView)
     if anyView.type == EmptyView.self {
       return MountedNull(anyView)

Sources/TokamakDOM/Environment/Environment.swift

@@ -18,3 +18,4 @@
 import TokamakCore
 
 public typealias Environment = TokamakCore.Environment
+public typealias EnvironmentObject = TokamakCore.EnvironmentObject

Sources/TokamakDemo/EnvironmentDemo.swift

@@ -18,17 +18,34 @@
 #if canImport(SwiftUI)
 import SwiftUI
 #else
+import OpenCombine
 import TokamakDOM
 #endif
 
+class TestEnvironment: ObservableObject {
+  @Published var envTest = "Hello, world!"
+  init() {}
+}
+
+struct EnvironmentObjectDemo: View {
+  @EnvironmentObject var testEnv: TestEnvironment
+
+  var body: some View {
+    Button(testEnv.envTest) {
+      testEnv.envTest = "EnvironmentObject modified."
+    }
+  }
+}
+
 struct EnvironmentDemo: View {
   @Environment(\.font) var font: Font?
+  @EnvironmentObject var testEnv: TestEnvironment
 
   var body: some View {
-    if let font = font {
-      return Text("\(String(describing: font))")
-    } else {
-      return Text("`font` environment not set.")
+    VStack {
+      Text(font == nil ? "`font` environment not set." : "\(String(describing: font!))")
+      Text(testEnv.envTest)
+      EnvironmentObjectDemo()
     }
   }
 }

Sources/TokamakDemo/TokamakDemo.swift

@@ -67,5 +67,6 @@ struct TokamakDemoView: View {
         }
       }
     }
+    .environmentObject(TestEnvironment())
   }
 }