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Groovy: A powerful, dynamic language for the JVM
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/*
 * Copyright 2003-2007 the original author or authors.
 *
 * 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 groovy.util;

import org.codehaus.groovy.control.CompilationFailedException;

import groovy.lang.Binding;
import groovy.lang.GroovyShell;

/**
 * Allow easy integration from Groovy into Java through convenience methods. 


 * 
 * This class is a simple helper on top of GroovyShell. You can use it to evaluate small
 * Groovy scripts that don't need large Binding objects. For example, this script 
 * executes with no errors: 
 *  * assert 10 == Eval.me(' 2 * 4 + 2')
 * assert 10 == Eval.x(2, ' x * 4 + 2')
 * 
 * 
 * @see GroovyShell
 * 
 * @author Dierk Koenig
 */

public class Eval {
    /**
     * Evaluates the specified String expression and returns the result. For example: 
     *      * assert 10 == Eval.me(' 2 * 4 + 2')
     * 
     * @param expression the Groovy expression to evaluate
     * @return the result of the expression
     * @throws CompilationFailedException if expression is not valid Groovy
     */
    public static Object me(final String expression) throws CompilationFailedException {
        return me(null, null, expression);
    }

    /**
     * Evaluates the specified String expression and makes the parameter available inside
     * the script, returning the result. For example, this code binds the 'x' variable: 
     *      * assert 10 == Eval.me('x', 2, ' x * 4 + 2')
     * 
     * @param expression the Groovy expression to evaluate
     * @return the result of the expression
     * @throws CompilationFailedException if expression is not valid Groovy
     */
    public static Object me(final String symbol, final Object object, final String expression) throws CompilationFailedException {
        Binding b = new Binding();
        b.setVariable(symbol, object);
        GroovyShell sh = new GroovyShell(b);
        return sh.evaluate(expression);
    }

    /**
     * Evaluates the specified String expression and makes the parameter available inside
     * the script bound to a variable named 'x', returning the result. For example, this 
     * code executes without failure: 
     *      * assert 10 == Eval.x(2, ' x * 4 + 2')
     * 
     * @param expression the Groovy expression to evaluate
     * @return the result of the expression
     * @throws CompilationFailedException if expression is not valid Groovy
     */
    public static Object x(final Object x, final String expression) throws CompilationFailedException {
        return me("x", x, expression);
    }

    /**
     * Evaluates the specified String expression and makes the first two parameters available inside
     * the script bound to variables named 'x' and 'y' respectively, returning the result. For example, 
     * this code executes without failure: 
     *      * assert 10 == Eval.xy(2, 4, ' x * y + 2')
     * 
     * @param expression the Groovy expression to evaluate
     * @return the result of the expression
     * @throws CompilationFailedException if expression is not valid Groovy
     */
    public static Object xy(final Object x, final Object y, final String expression) throws CompilationFailedException {
        Binding b = new Binding();
        b.setVariable("x", x);
        b.setVariable("y", y);
        GroovyShell sh = new GroovyShell(b);
        return sh.evaluate(expression);
    }

    /**
     * Evaluates the specified String expression and makes the first three parameters available inside
     * the script bound to variables named 'x', 'y', and 'z' respectively, returning the result. For 
     * example, this code executes without failure: 
     *      * assert 10 == Eval.xyz(2, 4, 2, ' x * y + z')
     * 
     * @param expression the Groovy expression to evaluate
     * @return the result of the expression
     * @throws CompilationFailedException if expression is not valid Groovy
     */
    public static Object xyz(final Object x, final Object y, final Object z, final String expression) throws CompilationFailedException {
        Binding b = new Binding();
        b.setVariable("x", x);
        b.setVariable("y", y);
        b.setVariable("z", z);
        GroovyShell sh = new GroovyShell(b);
        return sh.evaluate(expression);
    }
}