Added valueForKey filter

CHANGELOG.md

@@ -8,6 +8,7 @@
 - The `{% for %}` tag can now iterate over tuples, structures and classes via
   their stored properties.
 - Added `split` filter
+- Added `valueForKey` filter
 
 ### Bug Fixes
 

Sources/Extension.swift

@@ -26,6 +26,10 @@ open class Extension {
 
   /// Registers a template filter with the given name
   public func registerFilter(_ name: String, filter: @escaping (Any?, [Any?]) throws -> Any?) {
+    filters[name] = .arguments({ value, args, _ in try filter(value, args) })
+  }
+
+  public func registerFilter(_ name: String, filter: @escaping (Any?, [Any?], Context) throws -> Any?) {
     filters[name] = .arguments(filter)
   }
 }
@@ -58,28 +62,28 @@ class DefaultExtension: Extension {
     registerFilter("lowercase", filter: lowercase)
     registerFilter("join", filter: joinFilter)
     registerFilter("split", filter: splitFilter)
+    registerFilter("valueForKey", filter: valueForKeyFilter)
   }
 }
 
 
 protocol FilterType {
-  func invoke(value: Any?, arguments: [Any?]) throws -> Any?
+  func invoke(value: Any?, arguments: [Any?], context: Context) throws -> Any?
 }
 
 enum Filter: FilterType {
   case simple(((Any?) throws -> Any?))
-  case arguments(((Any?, [Any?]) throws -> Any?))
+  case arguments(((Any?, [Any?], Context) throws -> Any?))
 
-  func invoke(value: Any?, arguments: [Any?]) throws -> Any? {
+  func invoke(value: Any?, arguments: [Any?], context: Context) throws -> Any? {
     switch self {
     case let .simple(filter):
       if !arguments.isEmpty {
         throw TemplateSyntaxError("cannot invoke filter with an argument")
       }
-
       return try filter(value)
     case let .arguments(filter):
-      return try filter(value, arguments)
+      return try filter(value, arguments, context)
     }
   }
 }

Sources/Filters.swift

@@ -53,3 +53,14 @@ func splitFilter(value: Any?, arguments: [Any?]) throws -> Any? {
 
   return value
 }
+
+func valueForKeyFilter(value: Any?, arguments: [Any?], context: Context) throws -> Any? {
+  guard arguments.count == 1 else {
+    throw TemplateSyntaxError("'split' filter takes a single argument")
+  }
+
+  let key = stringify(arguments[0])
+  return try context.push(dictionary: ["filter_value": value as Any]) {
+    return try Variable("filter_value.\(key)").resolve(context)
+  }
+}

Sources/Variable.swift

@@ -36,7 +36,7 @@ class FilterExpression : Resolvable {
 
     return try filters.reduce(result) { x, y in
       let arguments = try y.1.map { try $0.resolve(context) }
-      return try y.0.invoke(value: x, arguments: arguments)
+      return try y.0.invoke(value: x, arguments: arguments, context: context)
     }
   }
 }

Tests/StencilTests/FilterSpec.swift

@@ -199,4 +199,18 @@ func testFilter() {
     }
   }
 
+  describe("valueForKey filter") {
+    $0.it("can get value for predefined key") {
+      let template = Template(templateString: "{{ value|valueForKey:\"name\" }}")
+      let result = try template.render(Context(dictionary: ["value": ["name": "One"]]))
+      try expect(result) == "One"
+    }
+
+    $0.it("can get value for runtime key") {
+      let template = Template(templateString: "{{ value|valueForKey:key }}")
+      let result = try template.render(Context(dictionary: ["key": "name", "value": ["name": "One"]]))
+      try expect(result) == "One"
+    }
+  }
+
 }