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/*
 * Copyright 2014 - 2018 Rafael Winterhalter
 *
 * 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 net.bytebuddy.implementation.bytecode.constant;

import net.bytebuddy.implementation.Implementation;
import net.bytebuddy.implementation.bytecode.StackManipulation;
import net.bytebuddy.implementation.bytecode.StackSize;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

/**
 * Represents a stack manipulation to load a {@code null} pointer onto the operand stack.
 */
public enum NullConstant implements StackManipulation {

    /**
     * The singleton instance.
     */
    INSTANCE(StackSize.SINGLE);

    /**
     * The size impact of loading the {@code null} reference onto the operand stack.
     */
    private final Size size;

    /**
     * Creates a null constant.
     *
     * @param size The size of the constant on the operand stack.
     */
    NullConstant(StackSize size) {
        this.size = size.toIncreasingSize();
    }

    /**
     * {@inheritDoc}
     */
    public boolean isValid() {
        return true;
    }

    /**
     * {@inheritDoc}
     */
    public Size apply(MethodVisitor methodVisitor, Implementation.Context implementationContext) {
        methodVisitor.visitInsn(Opcodes.ACONST_NULL);
        return size;
    }
}