feat(if): Support inequality operator

CHANGELOG.md

@@ -20,8 +20,8 @@
 - Variable lookup now supports introspection of Swift types. You can now lookup
   values of Swift structures and classes inside a Context.
 
-- If tags can now use prefix and infix operators such as `not`, `and`, `or` and
+- If tags can now use prefix and infix operators such as `not`, `and`, `or`,
-  `==`.
+  `==`, and `!=`.
 
     ```html+django
     {% if one or two and not three %}

Sources/Expression.swift

@@ -134,11 +134,11 @@ final class AndExpression: Expression, InfixOperator, CustomStringConvertible {
 }
 
 
-final class EqualityExpression: Expression, InfixOperator, CustomStringConvertible {
+class EqualityExpression: Expression, InfixOperator, CustomStringConvertible {
   let lhs: Expression
   let rhs: Expression
 
-  init(lhs: Expression, rhs: Expression) {
+  required init(lhs: Expression, rhs: Expression) {
     self.lhs = lhs
     self.rhs = rhs
   }
@@ -170,6 +170,17 @@ final class EqualityExpression: Expression, InfixOperator, CustomStringConvertib
 }
 
 
+class InequalityExpression: EqualityExpression {
+  override var description: String {
+    return "(\(lhs) != \(rhs))"
+  }
+
+  override func evaluate(context: Context) throws -> Bool {
+    return try !super.evaluate(context: context)
+  }
+}
+
+
 func toNumber(value: Any) -> Float80? {
     if let value = value as? Float {
         return Float80(value)

Sources/IfTag.swift

@@ -18,6 +18,7 @@ let operators: [Operator] = [
   .infix("and", 7, AndExpression.self),
   .prefix("not", 8, NotExpression.self),
   .infix("==", 10, EqualityExpression.self),
+  .infix("!=", 10, InequalityExpression.self),
 ]
 
 

Tests/StencilTests/ExpressionSpec.swift

@@ -162,7 +162,7 @@ func testExpressions() {
         }
 
         $0.it("evaluates to false with non equal lhs/rhs") {
-          print(expression)
+          try expect(expression.evaluate(context: Context(dictionary: ["lhs": "a", "rhs": "b"]))).to.beFalse()
         }
 
         $0.it("evaluates to true with nils") {
@@ -190,6 +190,18 @@ func testExpressions() {
         }
       }
 
+      $0.describe("inequality expression") {
+        let expression = try! parseExpression(components: ["lhs", "!=", "rhs"])
+
+        $0.it("evaluates to true with inequal lhs/rhs") {
+          try expect(expression.evaluate(context: Context(dictionary: ["lhs": "a", "rhs": "b"]))).to.beTrue()
+        }
+
+        $0.it("evaluates to false with equal lhs/rhs") {
+          try expect(expression.evaluate(context: Context(dictionary: ["lhs": "b", "rhs": "b"]))).to.beFalse()
+        }
+      }
+
       $0.describe("multiple expression") {
         let expression = try! parseExpression(components: ["one", "or", "two", "and", "not", "three"])
 

docs/builtins.rst

@@ -106,6 +106,17 @@ Will be treated as:
 
 .. note:: The equality operator only supports numerical, string and boolean types.
 
+``!=`` operator
+"""""""""""""""
+
+.. code-block:: html+django
+
+    {% if value != other_value %}
+      value is not equal to other_value
+    {% endif %}
+
+.. note:: The inequality operator only supports numerical, string and boolean types.
+
 ``ifnot``
 ~~~~~~~~~