From 7247d0a83dfb2c8ba82b7dbd1a75809105aa305f Mon Sep 17 00:00:00 2001
From: Ilya Puchka <ilyapuchka@gmail.com>
Date: Sat, 22 Sep 2018 16:04:57 +0100
Subject: [PATCH] Dynamic member lookup (via marker protocol)

---
 Sources/DynamicMemberLookup.swift     | 15 +++++++++++++
 Sources/Variable.swift                |  2 ++
 Tests/StencilTests/VariableSpec.swift | 31 ++++++++++++++++++++++++++-
 3 files changed, 47 insertions(+), 1 deletion(-)
 create mode 100644 Sources/DynamicMemberLookup.swift

diff --git a/Sources/DynamicMemberLookup.swift b/Sources/DynamicMemberLookup.swift
new file mode 100644
index 0000000..47aae01
--- /dev/null
+++ b/Sources/DynamicMemberLookup.swift
@@ -0,0 +1,15 @@
+/// Marker protocol so we can know which types support `@dynamicMemberLookup`. Add this to your own types that support
+/// lookup by String.
+public protocol DynamicMemberLookup {
+  /// Get a value for a given `String` key
+  subscript(dynamicMember member: String) -> Any? { get }
+}
+
+public extension DynamicMemberLookup where Self: RawRepresentable {
+  subscript(dynamicMember member: String) -> Any? {
+    switch member {
+    case "rawValue": return rawValue
+    default: return nil
+    }
+  }
+}
diff --git a/Sources/Variable.swift b/Sources/Variable.swift
index 995706c..ca2d245 100644
--- a/Sources/Variable.swift
+++ b/Sources/Variable.swift
@@ -110,6 +110,8 @@ public struct Variable: Equatable, Resolvable {
           return object.value(forKey: bit)
         }
       #endif
+    } else if let value = context as? DynamicMemberLookup {
+      return value[dynamicMember: bit]
     } else if let value = context {
       return Mirror(reflecting: value).getValue(for: bit)
     }
diff --git a/Tests/StencilTests/VariableSpec.swift b/Tests/StencilTests/VariableSpec.swift
index e834064..52b276d 100644
--- a/Tests/StencilTests/VariableSpec.swift
+++ b/Tests/StencilTests/VariableSpec.swift
@@ -30,6 +30,17 @@ private class Blog: WebSite {
   let featuring: Article? = Article(author: Person(name: "Jhon"))
 }
 
+@dynamicMemberLookup
+private struct DynamicStruct: DynamicMemberLookup {
+  subscript(dynamicMember member: String) -> Any? {
+    member == "test" ? "this is a dynamic response" : nil
+  }
+}
+
+private enum DynamicEnum: String, DynamicMemberLookup {
+  case someValue = "this is raw value"
+}
+
 final class VariableTests: XCTestCase {
   let context: Context = {
     let ext = Extension()
@@ -49,7 +60,11 @@ final class VariableTests: XCTestCase {
       ],
       "article": Article(author: Person(name: "Kyle")),
       "blog": Blog(),
-      "tuple": (one: 1, two: 2)
+      "tuple": (one: 1, two: 2),
+      "dynamic": [
+        "enum": DynamicEnum.someValue,
+        "struct": DynamicStruct()
+      ]
     ], environment: environment)
 #if os(OSX)
     context["object"] = Object()
@@ -158,6 +173,20 @@ final class VariableTests: XCTestCase {
     }
   }
 
+  func testDynamicMemberLookup() {
+    it("can resolve dynamic member lookup") {
+      let variable = Variable("dynamic.struct.test")
+      let result = try variable.resolve(self.context) as? String
+      try expect(result) == "this is a dynamic response"
+    }
+
+    it("can resolve dynamic enum rawValue") {
+      let variable = Variable("dynamic.enum.rawValue")
+      let result = try variable.resolve(self.context) as? String
+      try expect(result) == "this is raw value"
+    }
+  }
+
   func testReflection() {
     it("can resolve a property with reflection") {
       let variable = Variable("article.author.name")