New ThisIdentifier expression

This allows member expressions to use the 'this' keyword.

src/ol/expr/expressions.js

@@ -10,6 +10,7 @@ goog.provide('ol.expr.Math');
 goog.provide('ol.expr.MathOp');
 goog.provide('ol.expr.Member');
 goog.provide('ol.expr.Not');
+goog.provide('ol.expr.ThisIdentifier');
 
 
 
@@ -624,3 +625,24 @@ ol.expr.Not.prototype.evaluate = function(opt_scope, opt_fns, opt_this) {
 ol.expr.Not.prototype.getArgument = function() {
   return this.argument_;
 };
+
+
+
+/**
+ * An identifier for the 'this' keyword.
+ *
+ * @constructor
+ * @extends {ol.expr.Expression}
+ */
+ol.expr.ThisIdentifier = function() {};
+goog.inherits(ol.expr.ThisIdentifier, ol.expr.Expression);
+goog.addSingletonGetter(ol.expr.ThisIdentifier);
+
+
+/**
+ * @inheritDoc
+ */
+ol.expr.ThisIdentifier.prototype.evaluate =
+    function(opt_scope, opt_fns, opt_this) {
+  return opt_this;
+};

src/ol/expr/lexer.js

@@ -85,6 +85,7 @@ ol.expr.TokenType = {
   NUMERIC_LITERAL: 'Numeric',
   PUNCTUATOR: 'Punctuator',
   STRING_LITERAL: 'String',
+  THIS_IDENTIFIER: 'This',
   UNKNOWN: 'Unknown'
 };
 
@@ -515,7 +516,8 @@ ol.expr.Lexer.prototype.scanIdentifier_ = function(code) {
   if (id.length === 1) {
     type = ol.expr.TokenType.IDENTIFIER;
   } else if (this.isKeyword_(id)) {
-    type = ol.expr.TokenType.KEYWORD;
+    type = (id === 'this') ?
+        ol.expr.TokenType.THIS_IDENTIFIER : ol.expr.TokenType.KEYWORD;
   } else if (id === 'null') {
     type = ol.expr.TokenType.NULL_LITERAL;
   } else if (id === 'true' || id === 'false') {

src/ol/expr/parser.js

@@ -30,6 +30,7 @@ goog.require('ol.expr.Math');
 goog.require('ol.expr.MathOp');
 goog.require('ol.expr.Member');
 goog.require('ol.expr.Not');
+goog.require('ol.expr.ThisIdentifier');
 goog.require('ol.expr.Token');
 goog.require('ol.expr.TokenType');
 goog.require('ol.expr.UnexpectedToken');
@@ -198,6 +199,16 @@ ol.expr.Parser.prototype.createMemberExpression_ = function(object,
 };
 
 
+/**
+ * Create a 'this' identifier.
+ * @return {ol.expr.ThisIdentifier} The 'this' identifier.
+ * @private
+ */
+ol.expr.Parser.prototype.createThisIdentifier_ = function() {
+  return ol.expr.ThisIdentifier.getInstance();
+};
+
+
 /**
  * Create a unary expression.  The only true unary operator supported here is
  * "!".  For +/-, we apply the operator to literal expressions and return
@@ -434,6 +445,8 @@ ol.expr.Parser.prototype.parsePrimaryExpression_ = function(lexer) {
     expr = this.createLiteral_(token.value === 'true');
   } else if (type === ol.expr.TokenType.NULL_LITERAL) {
     expr = this.createLiteral_(null);
+  } else if (type === ol.expr.TokenType.THIS_IDENTIFIER) {
+    expr = this.createThisIdentifier_();
   } else {
     throw new ol.expr.UnexpectedToken(token);
   }

test/spec/ol/expr/expression.test.js

@@ -92,6 +92,12 @@ describe('ol.expr.parse()', function() {
       expect(expr.evaluate(scope)).to.be(42);
     });
 
+    it('parses member expressions in the \'this\' scope', function() {
+      var expr = ol.expr.parse('this.foo');
+      var thisScope = {foo: 'bar'};
+      expect(expr.evaluate(undefined, undefined, thisScope)).to.be('bar');
+    });
+
     it('consumes whitespace as expected', function() {
       var expr = ol.expr.parse(' foo . bar . baz ');
       expect(expr).to.be.a(ol.expr.Member);

test/spec/ol/expr/expressions.test.js

@@ -624,6 +624,25 @@ describe('ol.expr.Not', function() {
 });
 
 
+describe('ol.expr.ThisIdentifier', function() {
+
+  describe('#getInstance()', function() {
+    it('has a getInstance method to return the singleton', function() {
+      expect(ol.expr.ThisIdentifier.getInstance())
+          .to.be.a(ol.expr.ThisIdentifier);
+    });
+  });
+
+  describe('#evaluate()', function() {
+    it('evaluates to the passed scope', function() {
+      expect(ol.expr.ThisIdentifier.getInstance()
+          .evaluate(undefined, undefined, 'foo')).to.be('foo');
+    });
+  });
+
+});
+
+
 goog.require('ol.expr.Call');
 goog.require('ol.expr.Comparison');
 goog.require('ol.expr.ComparisonOp');
@@ -636,3 +655,4 @@ goog.require('ol.expr.Math');
 goog.require('ol.expr.MathOp');
 goog.require('ol.expr.Member');
 goog.require('ol.expr.Not');
+goog.require('ol.expr.ThisIdentifier');