Allow mirrorables in builder if/switch expressions (#26)

Author: davdroman

Sources/AtomicTransition/AtomicTransitionBuilder.swift

@@ -110,4 +110,85 @@ public struct AtomicTransitionBuilder {
         Combined(Combined(Combined(Combined(Combined(Combined(t1, t2), t3), t4), t5), t6), t7)
     }
     #endif
+
+    public static func buildOptional<T: AtomicTransition>(_ component: T?) -> _OptionalTransition<T> {
+        if let component = component {
+            return _OptionalTransition(component)
+        } else {
+            return _OptionalTransition(nil)
+        }
+    }
+
+    public static func buildEither<TrueTransition: AtomicTransition, FalseTransition: AtomicTransition>(first component: TrueTransition) -> _ConditionalTransition<TrueTransition, FalseTransition> {
+        _ConditionalTransition(trueTransition: component)
+    }
+
+    public static func buildEither<TrueTransition: AtomicTransition, FalseTransition: AtomicTransition>(second component: FalseTransition) -> _ConditionalTransition<TrueTransition, FalseTransition> {
+        _ConditionalTransition(falseTransition: component)
+    }
+}
+
+public struct _OptionalTransition<Transition: AtomicTransition>: AtomicTransition {
+    private let transition: Transition?
+
+    init(_ transition: Transition?) {
+        self.transition = transition
+    }
+
+    public func transition(_ view: TransientView, for operation: TransitionOperation, in container: Container) {
+        transition?.transition(view, for: operation, in: container)
+    }
 }
+
+extension _OptionalTransition: MirrorableAtomicTransition where Transition: MirrorableAtomicTransition {
+    public func mirrored() -> _OptionalTransition<Transition.Mirrored> {
+        .init(transition?.mirrored())
+    }
+}
+
+extension _OptionalTransition: Equatable where Transition: Equatable {}
+extension _OptionalTransition: Hashable where Transition: Hashable {}
+
+public struct _ConditionalTransition<TrueTransition: AtomicTransition, FalseTransition: AtomicTransition>: AtomicTransition {
+    private typealias Transition = _Either<TrueTransition, FalseTransition>
+    private let transition: Transition
+
+    init(trueTransition: TrueTransition) {
+        self.transition = .left(trueTransition)
+    }
+
+    init(falseTransition: FalseTransition) {
+        self.transition = .right(falseTransition)
+    }
+
+    public func transition(_ view: TransientView, for operation: TransitionOperation, in container: Container) {
+        switch transition {
+        case .left(let trueTransition):
+            trueTransition.transition(view, for: operation, in: container)
+        case .right(let falseTransition):
+            falseTransition.transition(view, for: operation, in: container)
+        }
+    }
+}
+
+extension _ConditionalTransition: MirrorableAtomicTransition where TrueTransition: MirrorableAtomicTransition, FalseTransition: MirrorableAtomicTransition {
+    public func mirrored() -> _ConditionalTransition<TrueTransition.Mirrored, FalseTransition.Mirrored> {
+        switch transition {
+        case .left(let trueTransition):
+            return .init(trueTransition: trueTransition.mirrored())
+        case .right(let falseTransition):
+            return .init(falseTransition: falseTransition.mirrored())
+        }
+    }
+}
+
+extension _ConditionalTransition: Equatable where TrueTransition: Equatable, FalseTransition: Equatable {}
+extension _ConditionalTransition: Hashable where TrueTransition: Hashable, FalseTransition: Hashable {}
+
+private enum _Either<Left, Right> {
+    case left(Left)
+    case right(Right)
+}
+
+extension _Either: Equatable where Left: Equatable, Right: Equatable {}
+extension _Either: Hashable where Left: Hashable, Right: Hashable {}

Sources/AtomicTransition/Mirror.swift

@@ -1,4 +1,4 @@
-/// A transition that executes only on insertion.
+/// A transition that executes only on insertion, but executes only on removal when mirrored.
 public struct MirrorInsertion<Transition: AtomicTransition>: AtomicTransition {
     private let transition: Transition
 
@@ -29,7 +29,7 @@ extension MirrorInsertion: MirrorableAtomicTransition where Transition: Mirrorab
 extension MirrorInsertion: Equatable where Transition: Equatable {}
 extension MirrorInsertion: Hashable where Transition: Hashable {}
 
-/// A transition that executes only on removal.
+/// A transition that executes only on removal, but executes only on insertion when mirrored.
 public struct MirrorRemoval<Transition: AtomicTransition>: AtomicTransition {
     private let transition: Transition
 

Sources/NavigationTransition/Asymmetric.swift

@@ -1,6 +1,6 @@
 import AtomicTransition
 
-/// A composite transition that uses a different transition for insertion versus removal.
+/// A composite transition that uses a different transition for push versus pop.
 public struct Asymmetric<PushTransition: NavigationTransition, PopTransition: NavigationTransition>: NavigationTransition {
     private let push: PushTransition
     private let pop: PopTransition
@@ -31,7 +31,7 @@ public struct Asymmetric<PushTransition: NavigationTransition, PopTransition: Na
 extension Asymmetric: Equatable where PushTransition: Equatable, PopTransition: Equatable {}
 extension Asymmetric: Hashable where PushTransition: Hashable, PopTransition: Hashable {}
 
-/// A transition that executes only on insertion.
+/// Used to define a transition that executes only on push.
 public struct OnPush<Transition: AtomicTransition>: NavigationTransition {
     private let transition: Transition
 
@@ -58,7 +58,7 @@ public struct OnPush<Transition: AtomicTransition>: NavigationTransition {
 extension OnPush: Equatable where Transition: Equatable {}
 extension OnPush: Hashable where Transition: Hashable {}
 
-/// A transition that executes only on removal.
+/// Used to define a transition that executes only on pop.
 public struct OnPop<Transition: AtomicTransition>: NavigationTransition {
     private let transition: Transition
 

Sources/NavigationTransition/Mirror.swift

@@ -1,5 +1,6 @@
 import AtomicTransition
 
+/// Used to define a transition that executes on push, and executes the mirrored version of said transition on pop.
 public struct MirrorPush<Transition: MirrorableAtomicTransition>: NavigationTransition {
     private let transition: Transition
 
@@ -17,6 +18,7 @@ public struct MirrorPush<Transition: MirrorableAtomicTransition>: NavigationTran
     }
 }
 
+/// Used to define a transition that executes on pop, and executes the mirrored version of said transition on push.
 public struct MirrorPop<Transition: MirrorableAtomicTransition>: NavigationTransition {
     private let transition: Transition
 

Sources/NavigationTransition/NavigationTransitionBuilder.swift

@@ -143,17 +143,15 @@ public struct _OptionalTransition<Transition: NavigationTransition>: NavigationT
 }
 
 public struct _ConditionalTransition<TrueTransition: NavigationTransition, FalseTransition: NavigationTransition>: NavigationTransition {
-    private let trueTransition: TrueTransition?
-    private let falseTransition: FalseTransition?
+    private typealias Transition = _Either<TrueTransition, FalseTransition>
+    private let transition: Transition
 
     init(trueTransition: TrueTransition) {
-        self.trueTransition = trueTransition
-        self.falseTransition = nil
+        self.transition = .left(trueTransition)
     }
 
     init(falseTransition: FalseTransition) {
-        self.trueTransition = nil
-        self.falseTransition = falseTransition
+        self.transition = .right(falseTransition)
     }
 
     public func transition(
@@ -162,7 +160,19 @@ public struct _ConditionalTransition<TrueTransition: NavigationTransition, False
         for operation: TransitionOperation,
         in container: Container
     ) {
-        trueTransition?.transition(from: fromView, to: toView, for: operation, in: container)
-        falseTransition?.transition(from: fromView, to: toView, for: operation, in: container)
+        switch transition {
+        case .left(let trueTransition):
+            trueTransition.transition(from: fromView, to: toView, for: operation, in: container)
+        case .right(let falseTransition):
+            falseTransition.transition(from: fromView, to: toView, for: operation, in: container)
+        }
     }
 }
+
+private enum _Either<Left, Right> {
+    case left(Left)
+    case right(Right)
+}
+
+extension _Either: Equatable where Left: Equatable, Right: Equatable {}
+extension _Either: Hashable where Left: Hashable, Right: Hashable {}