Rework the syntax to use brackets instead of a $

Author: djbe

CHANGELOG.md

@@ -8,7 +8,7 @@
   [Yonas Kolb](https://github.com/yonaskolb)
   [#214](https://github.com/stencilproject/Stencil/pull/214)
 - Variables now support indirect evaluation. For example, if you have a variable `key = "name"`, and an
-  object `item = ["name": "John"]`, then `{{ item.$key }}` will evaluate to "John".  
+  object `item = ["name": "John"]`, then `{{ item[key] }}` will evaluate to "John".  
   [David Jennes](https://github.com/djbe)
   [#215](https://github.com/stencilproject/Stencil/pull/215)
 

Sources/Variable.swift

@@ -50,8 +50,41 @@ public struct Variable : Equatable, Resolvable {
     self.variable = variable
   }
 
-  fileprivate func lookup() -> [String] {
-    return variable.characters.split(separator: ".").map(String.init)
+  // Split the lookup string and resolve references if possible
+  fileprivate func lookup(_ context: Context) throws -> [String] {
+    var current = ""
+    var referenceLevel = 0
+
+    var bits = [String]()
+    for c in variable {
+      switch c {
+      case "." where referenceLevel == 0:
+        bits += [current]
+        current = ""
+      case "[" where referenceLevel == 0:
+        bits += [current]
+        current = ""
+        referenceLevel += 1
+      case "[":
+        referenceLevel += 1
+        current.append(c)
+      case "]" where referenceLevel > 1:
+        current.append(c)
+        referenceLevel -= 1
+      case "]":
+        referenceLevel -= 1
+        let value = try Variable(current)
+          .resolve(context)
+          .flatMap { "\($0)" }
+        bits += [value ?? current]
+        current = ""
+      default:
+        current.append(c)
+      }
+    }
+    bits += [current]
+
+    return bits.filter { !$0.isEmpty }
   }
 
   /// Resolve the variable in the given context
@@ -75,16 +108,9 @@ public struct Variable : Equatable, Resolvable {
       return bool
     }
 
-    for var bit in lookup() {
+    for bit in try lookup(context) {
       current = normalize(current)
 
-      // try to evaluate bit if it's an indirection
-      if bit.hasPrefix("$"),
-        let resolved = try? Variable(String(bit.dropFirst())).resolve(context),
-        let property = resolved {
-        bit = "\(property)"
-      }
-
       if let context = current as? Context {
         current = context[bit]
       } else if let dictionary = current as? [String: Any] {

Tests/StencilTests/VariableSpec.swift

@@ -192,31 +192,31 @@ func testVariable() {
     $0.describe("Indirection") {
       $0.it("can resolve an indirect variable") {
         try context.push(dictionary: ["property": "name"]) {
-          let variable = Variable("$property")
+          let variable = Variable("[property]")
           let result = try variable.resolve(context) as? String
           try expect(result) == "Kyle"
         }
       }
 
       $0.it("can resolve an indirect variable via reflection") {
         try context.push(dictionary: ["property": "name"]) {
-          let variable = Variable("article.author.$property")
+          let variable = Variable("article.author[property]")
           let result = try variable.resolve(context) as? String
           try expect(result) == "Kyle"
         }
       }
 
       $0.it("can resolve an item from an array via it's indirect index") {
         try context.push(dictionary: ["property": 0]) {
-          let variable = Variable("contacts.$property")
+          let variable = Variable("contacts[property]")
           let result = try variable.resolve(context) as? String
           try expect(result) == "Katie"
         }
       }
 
       $0.it("can resolve an item from an array via unknown index") {
         try context.push(dictionary: ["property": 5]) {
-          let variable = Variable("contacts.$property")
+          let variable = Variable("contacts[property]")
           let result = try variable.resolve(context) as? String
           try expect(result).to.beNil()
         }
@@ -225,7 +225,7 @@ func testVariable() {
 #if os(OSX)
       $0.it("can resolve an indirect variable via KVO") {
         try context.push(dictionary: ["property": "name"]) {
-          let variable = Variable("object.$property")
+          let variable = Variable("object[property]")
           let result = try variable.resolve(context) as? String
           try expect(result) == "Foo"
         }
@@ -234,7 +234,7 @@ func testVariable() {
 
       $0.it("can resolve a value via reflection") {
         try context.push(dictionary: ["property": "articles"]) {
-          let variable = Variable("blog.$property.0.author.name")
+          let variable = Variable("blog[property].0.author.name")
           let result = try variable.resolve(context) as? String
           try expect(result) == "Kyle"
         }
@@ -246,7 +246,7 @@ func testVariable() {
           "prop2": 0,
           "prop3": "name"
         ]) {
-          let variable = Variable("blog.$prop1.$prop2.author.$prop3")
+          let variable = Variable("blog[prop1][prop2].author[prop3]")
           let result = try variable.resolve(context) as? String
           try expect(result) == "Kyle" 
         }

docs/templates.rst

@@ -31,7 +31,7 @@ For example, if `people` was an array:
     There are {{ people.count }} people. {{ people.first }} is the first
     person, followed by {{ people.1 }}.
 
-For indirect lookup, you can prefix a variable with `$`. That variable will be evaluated first, before the actual lookup will happen.
+For indirect lookup, you can surround a variable with brackets (`[]`). That variable will be evaluated first, before the actual lookup will happen.
 
 For example, if you have the following context:
 
@@ -46,7 +46,7 @@ For example, if you have the following context:
 
 .. code-block:: html+django
 
-    The result of {{ item.$key }} will be the same as {{ item.name }}. It will first evaluate the result of {{ key }}, and only then evaluate the lookup expression.
+    The result of {{ item[key] }} will be the same as {{ item.name }}. It will first evaluate the result of {{ key }}, and only then evaluate the lookup expression.
 
 Filters
 ~~~~~~~