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 * Copyright (c) 2012, 2014, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */
package com.oracle.graal.api.meta;

/**
 * Reflection operations on values represented as {@linkplain Constant constants}. All methods in
 * this interface require the VM to access the actual object encapsulated in {@link Kind#Object
 * object} constants. This access is not always possible, depending on kind of VM and the state that
 * the VM is in. Therefore, all methods can return {@code null} at any time, to indicate that the
 * result is not available at this point. The caller is responsible to check for {@code null}
 * results and handle them properly, e.g., not perform an optimization.
 */
public interface ConstantReflectionProvider {

    /**
     * Compares two constants for equality. The equality relationship is symmetric. Returns
     * {@link Boolean#TRUE true} if the two constants represent the same run time value,
     * {@link Boolean#FALSE false} if they are different. Returns {@code null} if the constants
     * cannot be compared at this point.
     */
    Boolean constantEquals(Constant x, Constant y);

    /**
     * Returns the length of the array constant. Returns {@code null} if the constant is not an
     * array, or if the array length is not available at this point.
     */
    Integer readArrayLength(Constant array);

    /**
     * Reads a value from the given array at the given index. Returns {@code null} if the constant
     * is not an array, if the index is out of bounds, or if the value is not available at this
     * point.
     */
    Constant readArrayElement(Constant array, int index);

    /**
     * Reads a value of this kind using a base address and a displacement. No bounds checking or
     * type checking is performed. Returns {@code null} if the value is not available at this point.
     *
     * @param base the base address from which the value is read.
     * @param displacement the displacement within the object in bytes
     * @return the read value encapsulated in a {@link Constant} object, or {@code null} if the
     *         value cannot be read.
     */
    Constant readUnsafeConstant(Kind kind, Constant base, long displacement);

    /**
     * Reads a primitive value using a base address and a displacement.
     *
     * @param kind the {@link Kind} of the returned {@link Constant} object
     * @param base the base address from which the value is read
     * @param displacement the displacement within the object in bytes
     * @param bits the number of bits to read from memory
     * @return the read value encapsulated in a {@link Constant} object of {@link Kind} kind
     */
    Constant readRawConstant(Kind kind, Constant base, long displacement, int bits);

    /**
     * Converts the given {@link Kind#isPrimitive() primitive} constant to a boxed
     * {@link Kind#Object object} constant, according to the Java boxing rules. Returns {@code null}
     * if the source is is not a primitive constant, or the boxed value is not available at this
     * point.
     */
    Constant boxPrimitive(Constant source);

    /**
     * Converts the given {@link Kind#Object object} constant to a {@link Kind#isPrimitive()
     * primitive} constant, according to the Java unboxing rules. Returns {@code null} if the source
     * is is not an object constant that can be unboxed, or the unboxed value is not available at
     * this point.
     */
    Constant unboxPrimitive(Constant source);

    /**
     * Returns the {@link ResolvedJavaType} for a {@link Class} object (or any other object regarded
     * as a class by the VM) encapsulated in the given constant. Returns {@code null} if the
     * constant does not encapsulate a class, or if the type is not available at this point.
     */
    ResolvedJavaType asJavaType(Constant constant);
}