groovy/src/main/org/codehaus/groovy/ast/expr/ElvisOperatorExpression.java

/*
 * 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 org.codehaus.groovy.ast.expr;

import org.codehaus.groovy.ast.GroovyCodeVisitor;

/**
 * Represents a short ternary expression x ?: y, which is equal 
 * to 
 * <pre>
 * def truePart = x
 * def booleanPart = truePart as boolean
 * booleanPart? truePart : y
 * </pre>
 * Even if x is no atomic expression, x will be evaluated only 
 * once. Example:
 * <pre>
 * class Foo { 
 *   def index=0 
 *   def getX(){ index++; return index }
 * }
 * def foo = new Foo()
 * def result = foo.x ?: "false case" 
 * assert foo.index == 1
 * assert result == 1 
 * <pre>
 * 
 * @author <a href="mailto:blackdrag@gmx.org">Jochen Theodorou</a>
 * @since 1.1
 */
public class ElvisOperatorExpression extends TernaryExpression {

    public ElvisOperatorExpression(Expression base, Expression falseExpression) {
        super(getBool(base), base, falseExpression);
    }
    
    private static BooleanExpression getBool(Expression base) {
       BooleanExpression be = new BooleanExpression(base);
       be.setSourcePosition(base);
       return be;
    }

    public void visit(GroovyCodeVisitor visitor) {
        visitor.visitShortTernaryExpression(this);
    }
    
    public Expression transformExpression(ExpressionTransformer transformer) {
        Expression ret = new ElvisOperatorExpression(
                transformer.transform(getTrueExpression()),
                transformer.transform(getFalseExpression()));
        ret.setSourcePosition(this);
        return ret; 
    }
}