lib/goog/reflect/reflect.js

1// Copyright 2009 The Closure Library Authors. All Rights Reserved.
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7// http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS-IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15/**
16 * @fileoverview Useful compiler idioms.
17 *
18 * @author johnlenz@google.com (John Lenz)
19 */
20
21goog.provide('goog.reflect');
22
23
24/**
25 * Syntax for object literal casts.
26 * @see http://go/jscompiler-renaming
27 * @see http://code.google.com/p/closure-compiler/wiki/
28 * ExperimentalTypeBasedPropertyRenaming
29 *
30 * Use this if you have an object literal whose keys need to have the same names
31 * as the properties of some class even after they are renamed by the compiler.
32 *
33 * @param {!Function} type Type to cast to.
34 * @param {Object} object Object literal to cast.
35 * @return {Object} The object literal.
36 */
37goog.reflect.object = function(type, object) {
38 return object;
39};
40
41
42/**
43 * To assert to the compiler that an operation is needed when it would
44 * otherwise be stripped. For example:
45 * <code>
46 * // Force a layout
47 * goog.reflect.sinkValue(dialog.offsetHeight);
48 * </code>
49 * @type {!Function}
50 */
51goog.reflect.sinkValue = function(x) {
52 goog.reflect.sinkValue[' '](x);
53 return x;
54};
55
56
57/**
58 * The compiler should optimize this function away iff no one ever uses
59 * goog.reflect.sinkValue.
60 */
61goog.reflect.sinkValue[' '] = goog.nullFunction;
62
63
64/**
65 * Check if a property can be accessed without throwing an exception.
66 * @param {Object} obj The owner of the property.
67 * @param {string} prop The property name.
68 * @return {boolean} Whether the property is accessible. Will also return true
69 * if obj is null.
70 */
71goog.reflect.canAccessProperty = function(obj, prop) {
72 /** @preserveTry */
73 try {
74 goog.reflect.sinkValue(obj[prop]);
75 return true;
76 } catch (e) {}
77 return false;
78};