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Closure Stylesheets is an extension to CSS that adds variables, functions, conditionals, and mixins to standard CSS. The tool also supports minification, linting, RTL flipping, and CSS class renaming.

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/*
 * Copyright 2009 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.css.compiler.ast;

/**
 * The idea behind the {@link Proxiable} interface is to improve performance of
 * compiler passes by eliminating unnecessary copying of AST subtrees. Passes
 * which perform a lot of copying should use this copy-on-write proxy creation
 * mechanism instead.
 *
 * {@link CssNode} classes which implement the {@link Proxiable} interface
 * create copy-on-write proxy objects. Created proxies reflect the state of the
 * proxied object until a mutation method is called on the proxy. When this
 * happens the proxy copies the original object's data, breaks the link to the
 * original and updates itself with the mutation.
 *
 * Proxy nodes will usually reflect any changes performed on the original
 * node. If this behavior is not desired -- say proxies should act as copies of
 * the original node -- there is a simple solution. Just replace the original
 * node with a proxy and use the original node as the backing node for all
 * proxies. This way the original node is hidden and all modifications go
 * through proxies. The example implementation:
 * {@link CssCustomFunctionNode.CssCustomFunctionNodeProxy#createProxy()}.
 * q
 *
 * @param  the type of the proxy object, it should be the same as of proxied
 *            object
 * @author [email protected] (Damian Gajda)
 */
public interface Proxiable {

    /**
     * Creates the proxy object. If the original object is immutable and does not
     * have any children, it can return itself.
     *
     * @return the proxy object
     */
    T createProxy();

}