Initial commit

.gitignore

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+.DS_Store
+/.build
+/Packages
+/*.xcodeproj
+xcuserdata/

Package.swift

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+// swift-tools-version:5.3
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "Swappable",
+    platforms: [.iOS(.v13)],
+    products: [
+        // Products define the executables and libraries a package produces, and make them visible to other packages.
+        .library(
+            name: "Swappable",
+            targets: ["Swappable"]),
+    ],
+    dependencies: [
+        // Dependencies declare other packages that this package depends on.
+        // .package(url: /* package url */, from: "1.0.0"),
+    ],
+    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 this package depends on.
+        .target(
+            name: "Swappable",
+            dependencies: []),
+        .testTarget(
+            name: "SwappableTests",
+            dependencies: ["Swappable"]),
+    ]
+)

README.md

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+# swappable
+
+A description of this package.

Sources/Swappable/Swappable.swift

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+import UIKit
+import SwiftUI
+
+extension EnvironmentObject {
+    var hasValue: Bool {
+        Mirror(reflecting: self).children.contains { ($0.value is ObjectType) }
+    }
+}
+
+class ViewSwap<S>: ObservableObject where S: View, S: Swappable {
+
+    init<V>(with customView: @escaping (S.InputType) -> V, insteadOf _: S.Type)
+    where V: View {
+        self.view = { AnyView(customView($0)) }
+    }
+
+    let view: (S.InputType) -> AnyView
+}
+
+struct SwappedIfNeeded<S>: View where S: View, S: Swappable {
+
+    @EnvironmentObject var swap: ViewSwap<S>
+
+    let input: S.InputType
+    let content: S.DefaultBody
+
+    init(input: S.InputType, content: S.DefaultBody) {
+        self.input = input
+        self.content = content
+    }
+
+    var body: some View {
+        Group {
+            if _swap.hasValue {
+                swap.view(input)
+            } else {
+                content
+            }
+        }
+    }
+}
+
+
+public protocol Swappable {
+
+    associatedtype InputType
+    var input: InputType { get }
+    init(input: InputType)
+
+    associatedtype DefaultBody : View
+    @ViewBuilder var defaultBody: DefaultBody { get }
+}
+
+public extension View {
+
+    func swapView<V, S>(_ initV : @escaping (S.InputType) -> V, insteadOf typeS: S.Type) -> some View
+    where S: View, S: Swappable,
+          V: View {
+        environmentObject(ViewSwap<S>(with: initV, insteadOf: typeS))
+    }
+
+    @available(*, unavailable, message: "Init parameters must match!")
+    func swapView<V, S, P>(_ initV : (P) -> V, insteadOf typeS: S.Type) -> some View
+    where S: View, S: Swappable,
+          V: View {
+        self
+    }
+}
+
+extension Swappable where Self: View {
+
+    var body: some View {
+        SwappedIfNeeded<Self>(input: input, content: defaultBody)
+    }
+}

Tests/LinuxMain.swift

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+import XCTest
+
+import swappableTests
+
+var tests = [XCTestCaseEntry]()
+tests += swappableTests.allTests()
+XCTMain(tests)

Tests/SwappableTests/SwappableTests.swift

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+import XCTest
+@testable import Swappable
+
+final class SwappableTests: XCTestCase {
+
+    static var allTests: [(String, ()->())] = []
+}

Tests/SwappableTests/XCTestManifests.swift

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+import XCTest
+
+#if !canImport(ObjectiveC)
+public func allTests() -> [XCTestCaseEntry] {
+    return [
+        testCase(swappableTests.allTests),
+    ]
+}
+#endif