/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you 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;

/**
 * This class is a place holder for an empty expression. 
 * Empty expression are used in closures lists like (;). During
 * class Generation this expression should be either ignored or
 * replace with a null value.
 *   
 * @author Jochen Theodorou
 * @see org.codehaus.groovy.ast.stmt.EmptyStatement
 */
public class EmptyExpression extends Expression {
    public static final EmptyExpression INSTANCE = new EmptyExpression();

    public Expression transformExpression(ExpressionTransformer transformer) {
        return this;
    }

    public void visit(GroovyCodeVisitor visitor) {
        return;
    }
}

/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you 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.AnnotationNode;
import org.codehaus.groovy.ast.ClassNode;
import org.codehaus.groovy.ast.GroovyCodeVisitor;

import java.util.List;

/**
 * This class is a place holder for an empty expression. 
 * Empty expression are used in closures lists like (;). During
 * class Generation this expression should be either ignored or
 * replace with a null value.
 *   
 * @author Jochen Theodorou
 * @see org.codehaus.groovy.ast.stmt.EmptyStatement
 */
public class EmptyExpression extends Expression {
    public static final EmptyExpression INSTANCE = new EmptyExpression() {
        @Override
        public void setType(ClassNode t) {
            throw createUnsupportedOperationException();
        }

        @Override
        public void addAnnotation(AnnotationNode value) {
            throw createUnsupportedOperationException();
        }

        @Override
        public void addAnnotations(List<AnnotationNode> annotations) {
            throw createUnsupportedOperationException();
        }

        @Override
        public void setSynthetic(boolean synthetic) {
            throw createUnsupportedOperationException();
        }

        @Override
        public void setDeclaringClass(ClassNode declaringClass) {
            throw createUnsupportedOperationException();
        }

        @Override
        public void setHasNoRealSourcePosition(boolean value) {
            throw createUnsupportedOperationException();
        }

        private UnsupportedOperationException createUnsupportedOperationException() {
            return new UnsupportedOperationException("EmptyExpression.INSTANCE is immutable");
        }
    };

    public Expression transformExpression(ExpressionTransformer transformer) {
        return this;
    }

    public void visit(GroovyCodeVisitor visitor) {
        return;
    }
}

Make EmptyExpression.INSTANCE immutable