NamedOperation.java

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/*
   Copyright 2015 Attila Szegedi

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package jdk.dynalink;

import java.util.Objects;

/**
 * Operation that associates a name with another operation. Typically used with
 * operations that normally take a name or an index to bind them to a fixed
 * name. E.g.
 * <pre>
 *     new NamedOperation(
 *         new NamespaceOperation(
 *             StandardOperation.GET,
 *             StandardNamespace.PROPERTY),
 *         "color")
 * </pre>
 * will be a named operation for getting the property named "color" on the
 * object it is applied to, and
 * <pre>
 *     new NamedOperation(
 *         new NamespaceOperation(
 *             StandardOperation.GET,
 *             StandardNamespace.ELEMENT),
 *         3)
 * </pre>
 * will be a named operation for getting the element at index 3 from the collection
 * it is applied to ("name" in this context is akin to "address" and encompasses both
 * textual names, numeric indices, or any other kinds of addressing that linkers can
 * understand). In these cases, the expected signature of the call site for the
 * operation will change to no longer include the name parameter. Specifically,
 * the documentation for all {@link StandardOperation} members describes how
 * they are affected by being incorporated into a named operation.
 * <p>While {@code NamedOperation} can be constructed directly, it is often convenient
 * to use the {@link Operation#named(Object)} factory method instead, e.g.:
 * <pre>
 *    StandardOperation.GET
 *        .withNamespace(StandardNamespace.ELEMENT),
 *        .named(3)
 *     )
 * </pre>
 * <p>
 * Even though {@code NamedOperation} is most often used with {@link NamespaceOperation} as
 * its base, it can have other operations as its base too (except another named operation).
 * Specifically, {@link StandardOperation#CALL} as well as {@link StandardOperation#NEW} can
 * both be used with {@code NamedOperation} directly. The contract for these operations is such
 * that when they are used as named operations, their name is only used for diagnostic messages,
 * usually containing the textual representation of the source expression that retrieved the
 * callee, e.g. {@code StandardOperation.CALL.named("window.open")}.
 * </p>
 */
public final class NamedOperation implements Operation {
    private final Operation baseOperation;
    private final Object name;

    /**
     * Creates a new named operation.
     * @param baseOperation the base operation that is associated with a name.
     * @param name the name associated with the base operation. Note that the
     * name is not necessarily a string, but can be an arbitrary object. As the
     * name is used for addressing, it can be an {@link Integer} when meant
     * to be used as an index into an array or list etc.
     * @throws NullPointerException if either {@code baseOperation} or
     * {@code name} is null.
     * @throws IllegalArgumentException if {@code baseOperation} is itself a
     * {@code NamedOperation}.
     */
    public NamedOperation(final Operation baseOperation, final Object name) {
        if (baseOperation instanceof NamedOperation) {
            throw new IllegalArgumentException("baseOperation is a NamedOperation");
        }
        this.baseOperation = Objects.requireNonNull(baseOperation, "baseOperation is null");
        this.name = Objects.requireNonNull(name, "name is null");
    }

    /**
     * Returns the base operation of this named operation.
     * @return the base operation of this named operation.
     */
    public Operation getBaseOperation() {
        return baseOperation;
    }

    /**
     * Returns the name of this named operation.
     * @return the name of this named operation.
     */
    public Object getName() {
        return name;
    }

    /**
     * Finds or creates a named operation that differs from this one only in the name.
     * @param newName the new name to replace the old name with.
     * @return a named operation with the changed name.
     * @throws NullPointerException if the name is null.
     */
    public final NamedOperation changeName(final String newName) {
        return new NamedOperation(baseOperation, newName);
    }

    /**
     * Compares this named operation to another object. Returns true if the
     * other object is also a named operation, and both their base operations
     * and name are equal.
     */
    @Override
    public boolean equals(final Object obj) {
        if (obj instanceof NamedOperation) {
            final NamedOperation other = (NamedOperation)obj;
            return baseOperation.equals(other.baseOperation) && name.equals(other.name);
        }
        return false;
    }

    /**
     * Returns the hash code of this named operation. It is defined to be equal
     * to {@code baseOperation.hashCode() + 31 * name.hashCode()}.
     */
    @Override
    public int hashCode() {
        return baseOperation.hashCode() + 31 * name.hashCode();
    }

    /**
     * Returns the string representation of this named operation. It is defined
     * to be equal to {@code baseOperation.toString() + ":" + name.toString()}.
     */
    @Override
    public String toString() {
        return baseOperation.toString() + ":" + name.toString();
    }

    /**
     * If the passed operation is a named operation, returns its
     * {@link #getBaseOperation()}, otherwise returns the operation as is.
     * @param op the operation
     * @return the base operation of the passed operation.
     */
    public static Operation getBaseOperation(final Operation op) {
        return op instanceof NamedOperation ? ((NamedOperation)op).baseOperation : op;
    }

    /**
     * If the passed operation is a named operation, returns its
     * {@link #getName()}, otherwise returns null. Note that a named operation
     * object can never have a null name, therefore returning null is indicative
     * that the passed operation is not, in fact, a named operation.
     * @param op the operation
     * @return the name in the passed operation, or null if it is not a named
     * operation.
     */
    public static Object getName(final Operation op) {
        return op instanceof NamedOperation ? ((NamedOperation)op).name : null;
    }
}