Merge commit '7621e2f8dec938cf48181c8b10afc9b01f444e68' into beta

submodules/ComponentFlow/Source/Components/ZStack.swift

@@ -0,0 +1,49 @@
+import Foundation
+import UIKit
+
+public final class ZStack<ChildEnvironment: Equatable>: CombinedComponent {
+    public typealias EnvironmentType = ChildEnvironment
+
+    private let items: [AnyComponentWithIdentity<ChildEnvironment>]
+
+    public init(_ items: [AnyComponentWithIdentity<ChildEnvironment>]) {
+        self.items = items
+    }
+
+    public static func ==(lhs: ZStack<ChildEnvironment>, rhs: ZStack<ChildEnvironment>) -> Bool {
+        if lhs.items != rhs.items {
+            return false
+        }
+        return true
+    }
+
+    public static var body: Body {
+        let children = ChildMap(environment: ChildEnvironment.self, keyedBy: AnyHashable.self)
+
+        return { context in
+            let updatedChildren = context.component.items.map { item in
+                return children[item.id].update(
+                    component: item.component, environment: {
+                        context.environment[ChildEnvironment.self]
+                    },
+                    availableSize: context.availableSize,
+                    transition: context.transition
+                )
+            }
+
+            var size = CGSize(width: 0.0, height: 0.0)
+            for child in updatedChildren {
+                size.width = max(size.width, child.size.width)
+                size.height = max(size.height, child.size.height)
+            }
+
+            for child in updatedChildren {
+                context.add(child
+                    .position(child.size.centered(in: CGRect(origin: CGPoint(), size: size)).center)
+                )
+            }
+
+            return size
+        }
+    }
+}