Allow using collection accessors on strings (#245)

* allow using collection accessors on strings

* refactored resolving collection accessors

* refactored to fileprivate function

* Update Variable.swift

* Update templates.rst

CHANGELOG.md

@@ -26,6 +26,10 @@
   [Ilya Puchka](https://github.com/ilyapuchka)
   [#243](https://github.com/stencilproject/Stencil/pull/243)
 
+- Now you can access string characters by index or get string length the same was as if it was an array, i.e. `{{ 'string'.first }}`, `{{ 'string'.last }}`, `{{ 'string'.1 }}`, `{{ 'string'.count }}`.  
+  [Ilya Puchka](https://github.com/ilyapuchka)
+  [#245](https://github.com/stencilproject/Stencil/pull/245)
+
 ### Internal Changes
 
 - Updated the codebase to use Swift 4 features.  

Sources/Variable.swift

@@ -87,19 +87,9 @@ public struct Variable : Equatable, Resolvable {
           current = dictionary[bit]
         }
       } else if let array = current as? [Any] {
-        if let index = Int(bit) {
-          if index >= 0 && index < array.count {
-            current = array[index]
-          } else {
-            current = nil
-          }
-        } else if bit == "first" {
-          current = array.first
-        } else if bit == "last" {
-          current = array.last
-        } else if bit == "count" {
-          current = array.count
-        }
+        current = resolveCollection(array, bit: bit)
+      } else if let string = current as? String {
+        current = resolveCollection(string, bit: bit)
       } else if let object = current as? NSObject {  // NSKeyValueCoding
         #if os(Linux)
           return nil
@@ -128,6 +118,24 @@ public struct Variable : Equatable, Resolvable {
   }
 }
 
+private func resolveCollection<T: Collection>(_ collection: T, bit: String) -> Any? {
+  if let index = Int(bit) {
+    if index >= 0 && index < collection.count {
+      return collection[collection.index(collection.startIndex, offsetBy: index)]
+    } else {
+      return nil
+    }
+  } else if bit == "first" {
+    return collection.first
+  } else if bit == "last" {
+    return collection[collection.index(collection.endIndex, offsetBy: -1)]
+  } else if bit == "count" {
+    return collection.count
+  } else {
+    return nil
+  }
+}
+
 /// A structure used to represet range of two integer values expressed as `from...to`.
 /// Values should be numbers (they will be converted to integers).
 /// Rendering this variable produces array from range `from...to`.

Tests/StencilTests/VariableSpec.swift

@@ -86,42 +86,98 @@ func testVariable() {
       try expect(result) == "Kyle"
     }
 
-    $0.it("can resolve an item from a dictionary") {
-      let variable = Variable("profiles.github")
-      let result = try variable.resolve(context) as? String
-      try expect(result) == "kylef"
+    $0.context("given string") {
+      $0.it("can resolve an item via it's index") {
+        let variable = Variable("name.0")
+        let result = try variable.resolve(context) as? Character
+        try expect(result) == "K"
+
+        let variable1 = Variable("name.1")
+        let result1 = try variable1.resolve(context) as? Character
+        try expect(result1) == "y"
+      }
+
+      $0.it("can resolve an item via unknown index") {
+        let variable = Variable("name.5")
+        let result = try variable.resolve(context) as? Character
+        try expect(result).to.beNil()
+
+        let variable1 = Variable("name.-5")
+        let result1 = try variable1.resolve(context) as? Character
+        try expect(result1).to.beNil()
+      }
+
+      $0.it("can resolve the first item") {
+        let variable = Variable("name.first")
+        let result = try variable.resolve(context) as? Character
+        try expect(result) == "K"
+      }
+
+      $0.it("can resolve the last item") {
+        let variable = Variable("name.last")
+        let result = try variable.resolve(context) as? Character
+        try expect(result) == "e"
+      }
+
+      $0.it("can get the characters count") {
+        let variable = Variable("name.count")
+        let result = try variable.resolve(context) as? Int
+        try expect(result) == 4
+      }
     }
 
-    $0.it("can resolve an item from an array via it's index") {
-      let variable = Variable("contacts.0")
-      let result = try variable.resolve(context) as? String
-      try expect(result) == "Katie"
+    $0.context("given dictionary") {
+      $0.it("can resolve an item") {
+        let variable = Variable("profiles.github")
+        let result = try variable.resolve(context) as? String
+        try expect(result) == "kylef"
+      }
+
+      $0.it("can get the count") {
+        let variable = Variable("profiles.count")
+        let result = try variable.resolve(context) as? Int
+        try expect(result) == 1
+      }
+    }
+
+    $0.context("given array") {
+      $0.it("can resolve an item via it's index") {
+        let variable = Variable("contacts.0")
+        let result = try variable.resolve(context) as? String
+        try expect(result) == "Katie"
 
         let variable1 = Variable("contacts.1")
         let result1 = try variable1.resolve(context) as? String
         try expect(result1) == "Carlton"
-    }
+      }
 
-    $0.it("can resolve an item from an array via unknown index") {
-      let variable = Variable("contacts.5")
-      let result = try variable.resolve(context) as? String
-      try expect(result).to.beNil()
+      $0.it("can resolve an item via unknown index") {
+        let variable = Variable("contacts.5")
+        let result = try variable.resolve(context) as? String
+        try expect(result).to.beNil()
 
-      let variable1 = Variable("contacts.-5")
-      let result1 = try variable1.resolve(context) as? String
-      try expect(result1).to.beNil()
-    }
+        let variable1 = Variable("contacts.-5")
+        let result1 = try variable1.resolve(context) as? String
+        try expect(result1).to.beNil()
+      }
 
-    $0.it("can resolve the first item from an array") {
-      let variable = Variable("contacts.first")
-      let result = try variable.resolve(context) as? String
-      try expect(result) == "Katie"
-    }
+      $0.it("can resolve the first item") {
+        let variable = Variable("contacts.first")
+        let result = try variable.resolve(context) as? String
+        try expect(result) == "Katie"
+      }
 
-    $0.it("can resolve the last item from an array") {
-      let variable = Variable("contacts.last")
-      let result = try variable.resolve(context) as? String
-      try expect(result) == "Carlton"
+      $0.it("can resolve the last item") {
+        let variable = Variable("contacts.last")
+        let result = try variable.resolve(context) as? String
+        try expect(result) == "Carlton"
+      }
+
+      $0.it("can get the count") {
+        let variable = Variable("contacts.count")
+        let result = try variable.resolve(context) as? Int
+        try expect(result) == 2
+      }
     }
 
     $0.it("can resolve a property with reflection") {
@@ -130,12 +186,6 @@ func testVariable() {
       try expect(result) == "Kyle"
     }
 
-    $0.it("can get the count of a dictionary") {
-      let variable = Variable("profiles.count")
-      let result = try variable.resolve(context) as? Int
-      try expect(result) == 1
-    }
-
 #if os(OSX)
     $0.it("can resolve a value via KVO") {
       let variable = Variable("object.title")

docs/templates.rst

@@ -20,9 +20,9 @@ following lookup:
 
 - Context lookup
 - Dictionary lookup
-- Array lookup (first, last, count, index)
+- Array and string lookup (first, last, count, by index)
 - Key value coding lookup
-- Type introspection
+- Type introspection (via ``Mirror``)
 
 For example, if `people` was an array: