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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2023 Saxonica Limited
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package net.sf.saxon.om;

import net.sf.saxon.str.UnicodeString;
import net.sf.saxon.value.*;

/**
 * A sequence containing exactly one item. The main use of this class is in declaring the expected arguments
 * of reflexive method calls, where the use of One(T) rather than T emphasizes that the value must not be null/empty,
 * and generates type-checking code to ensure that it is not empty.
 *
 * To extract the wrapped item, use {@link #head()}.
 */
public class One extends ZeroOrOne {

    /**
     * Create an instance of the class
     * @param item The single item to be contained in the sequence. Must not be null.
     * @throws NullPointerException if item is null.
     */

    public One(T item) {
        super(item);
        if (item == null) {
            throw new NullPointerException();
        }
    }

    /**
     * Convenience function to create a singleton boolean value
     * @param value the boolean value
     * @return the boolean value wrapped as a One<BooleanValue>
     */

    public static One bool (boolean value) {
        return new One<>(BooleanValue.get(value));
    }

    /**
     * Convenience function to create a singleton string value
     * @param value the string value.. If null, the result will represent a zero-length string
     * @return the string value wrapped as a One<StringValue>
     */

    public static One string (String value) {
        return new One<>(new StringValue(value));
    }

    /**
     * Convenience function to create a singleton string value
     *
     * @param value the string value.. If null, the result will represent a zero-length string
     * @return the string value wrapped as a One<StringValue>
     */

    public static One string(UnicodeString value) {
        return new One<>(new StringValue(value));
    }

    /**
     * Convenience function to create a singleton integer value
     * @param value the integer value
     * @return the integer value wrapped as a One<IntegerValue>
     */

    public static One integer (long value) {
        return new One<>(new Int64Value(value));
    }

    /**
     * Convenience function to create a singleton double value
     *
     * @param value the double value
     * @return the double value wrapped as a One<DoubleValue>
     */

    public static One dbl(double value) {
        return new One<>(new DoubleValue(value));
    }
}