Implement AnyView.init(_fromValue:)

Package.swift

@@ -18,13 +18,15 @@ let package = Package(
         // Dependencies declare other packages that this package depends on.
         // .package(url: /* package url */, from: "1.0.0"),
         .package(url: "https://github.com/Cosmo/CoreGraphicsShim.git", .branch("master")),
+        .package(url: "https://github.com/nerdsupremacist/AssociatedTypeRequirementsKit.git", from: "0.2.0"),
     ],
     targets: [
         // Targets are the basic building blocks of a package. A target can define a module or a test suite.
         // Targets can depend on other targets in this package, and on products in packages which this package depends on.
         .target(
             name: "OpenSwiftUI",
-            dependencies: ["CoreGraphicsShim"]),
+            dependencies: ["CoreGraphicsShim", "AssociatedTypeRequirementsKit"]),
+
         .testTarget(
             name: "OpenSwiftUITests",
             dependencies: ["OpenSwiftUI"]),

README.md

@@ -159,7 +159,7 @@ Xcode 11.2 or higher is required.
 
 | Status | Name | Notes |
 | --- | --- | --- |
-| ⚠️ | `struct AnyView` | `init?(_fromValue value: Any)` missing. |
+| ✅ | `struct AnyView` | |
 | ✅ | `struct TupleView` | |
 
 ### Drawing and Animation

Sources/OpenSwiftUI/Associated Types/ViewAssociatedTypeRequirementsVisitor.swift

@@ -0,0 +1,20 @@
+import AssociatedTypeRequirementsVisitor
+
+/**
+  **For internal use only.** Use to be able to call a function on a view where you don't know the concrete type at Compile Time.
+ Implement `callAsFunction` and a version that can take `Any` will be included as an extension.
+
+ Useful for occassions where your intuition is to cast `Any` to `View`, but Swift will stop you due to the associated type requirement.
+
+ ```swift
+ guard let view = view as? View else { return }
+ // Do something
+ ```
+ */
+protocol ViewAssociatedTypeRequirementsVisitor: AssociatedTypeRequirementsVisitor {
+    associatedtype Visitor = ViewAssociatedTypeRequirementsVisitor
+    associatedtype Input = View
+    associatedtype Output
+
+    func callAsFunction<T : View>(_ value: T) -> Output
+}

Sources/OpenSwiftUI/Views/AnyView+initFromValue.swift

@@ -0,0 +1,18 @@
+import Foundation
+
+extension AnyView {
+    public init?(_fromValue value: Any) {
+        guard let view = ViewTypeEraser.shared(value) else { return nil }
+        self = view
+    }
+}
+
+private struct ViewTypeEraser: ViewAssociatedTypeRequirementsVisitor {
+    func callAsFunction<T: View>(_ value: T) -> AnyView {
+        return AnyView(value)
+    }
+}
+
+extension ViewTypeEraser {
+    static let shared = ViewTypeEraser()
+}

Sources/OpenSwiftUI/Views/AnyView.swift

@@ -17,10 +17,6 @@ public struct AnyView: View {
         _storage = AnyViewStorage<V>(view)
     }
 
-    public init?(_fromValue value: Any) {
-        fatalError()
-    }
-
     public typealias Body = Never
     public var body: Never {
         fatalError()

Tests/OpenSwiftUITests/OpenSwiftUITests.swift

@@ -8,15 +8,35 @@ final class OpenSwiftUITests: XCTestCase {
             Text("World")
         }
 
-        let body = HStack {
-            if true {
-                Text("Hello")
-            }
-            Text("World")
+    }
+
+    func testAnyViewFromValueWithInDoesNotYieldView() {
+        let anyView = AnyView(_fromValue: 42)
+        XCTAssertNil(anyView)
+    }
+
+    func testAnyViewFromValueWithTextYieldsAnyView() {
+        let expectedText = "Hello"
+        let value: Any = Text(expectedText)
+        let anyView = AnyView(_fromValue: value)
+        XCTAssertNotNil(anyView)
+
+        guard let storage = anyView?._storage as? AnyViewStorage<Text> else {
+            XCTFail("View storage is not an AnyViewStorage of Text")
+            return
+        }
+
+        switch storage._view._storage {
+        case .verbatim(let string):
+            XCTAssertEqual(string, expectedText)
+        case .anyTextStorage(let storage):
+            XCTAssertEqual(storage.storage, expectedText)
         }
     }
 
     static var allTests = [
         ("testExample", testExample),
+        ("testAnyViewFromValueWithInDoesNotYieldView", testAnyViewFromValueWithInDoesNotYieldView),
+        ("testAnyViewFromValueWithTextYieldsAnyView", testAnyViewFromValueWithTextYieldsAnyView),
     ]
 }