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The Protelis language interpreter

There is a newer version: 17.6.0

/*
 * Copyright (C) 2021, Danilo Pianini and contributors listed in the project's build.gradle.kts or pom.xml file.
 *
 * This file is part of Protelis, and is distributed under the terms of the GNU General Public License,
 * with a linking exception, as described in the file LICENSE.txt in this project's top directory.
 */
package org.protelis.lang.interpreter.util;

/**
 * Utility class that OpN classes use for reporting certain failure patterns.
 */
public final class OpUtils {

    private OpUtils() {
    }

    /**
     * This method builds a meaningful exception and throws it immediately.
     *
     * @param op
     *            The name of the operation
     * @param a
     *            The arguments that have been passed, and that made the
     *            operation fail.
     * @param 
     *            Return type. This function never returns, this type is a
     *            placeholder that allows you to write stuff like
     *            "return unsupported(op, args)".
     * @throws UnsupportedOperationException
     *             ALWAYS
     * @return Nothing, since it throws an exception
     */
    public static  T unsupported(final String op, final Object... a) {
        final StringBuilder msg = new StringBuilder("Nobody told me how to run operator ");
        msg.append(op);
        if (a.length > 0) {
            msg.append(" with the following parameters: ");
            boolean first = true;
            for (final Object o : a) {
                if (first) {
                    first = false;
                } else {
                    msg.append("; ");
                }
                if (o == null) {
                    msg.append("null");
                } else {
                    quoteIfStringy(msg, o)
                        .append(o);
                    quoteIfStringy(msg, o)
                        .append(": ")
                        .append(o.getClass().getName());
                }
            }
            msg.append('.');
        }
        throw new UnsupportedOperationException(msg.toString());
    }

    private static StringBuilder quoteIfStringy(final StringBuilder builder, final Object o) {
        return o instanceof CharSequence ? builder.append('"') : builder;
    }
}