src/java/org/apache/cassandra/cql3/functions/ScalarFunction.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.cassandra.cql3.functions;

import java.nio.ByteBuffer;
import java.util.List;

import org.apache.cassandra.exceptions.InvalidRequestException;
import org.apache.cassandra.transport.ProtocolVersion;

/**
 * Determines a single output value based on any number of input values.
 */
public interface ScalarFunction extends Function
{
    public boolean isCalledOnNullInput();

    /**
     * Checks if the function is monotonic.
     *
     *<p>A function is monotonic if it is either entirely nonincreasing or nondecreasing given an ordered set of inputs.</p>
     *
     * @return {@code true} if the function is monotonic {@code false} otherwise.
     */
    public default boolean isMonotonic()
    {
        return false;
    }

    /**
     * Applies this function to the specified parameter.
     *
     * @param protocolVersion protocol version used for parameters and return value
     * @param parameters the input parameters
     * @return the result of applying this function to the parameter
     * @throws InvalidRequestException if this function cannot not be applied to the parameter
     */
    public ByteBuffer execute(ProtocolVersion protocolVersion, List<ByteBuffer> parameters) throws InvalidRequestException;

    /**
     * Does a partial application of the function. That is, given only some of the parameters of the function provided,
     * return a new function that only expect the parameters not provided.
     * <p>
     * To take an example, if you consider the function
     * <pre>
     *     text foo(int a, text b, text c, int d)
     * </pre>
     * then {@code foo.partialApplication([3, <ommitted>, 'bar', <omitted>])} will return a function {@code bar} of signature:
     * <pre>
     *     text bar(text b, int d)
     * </pre>
     * and such that for any value of {@code b} and {@code d}, {@code bar(b, d) == foo(3, b, 'bar', d)}.
     *
     * @param protocolVersion protocol version used for parameters
     * @param partialParameters a list of input parameters for the function where some parameters can be {@link #UNRESOLVED}.
     *                          The input <b>must</b> be of size {@code this.argsType().size()}. For convenience, it is
     *                          allowed both to pass a list with all parameters being {@link #UNRESOLVED} (the function is
     *                          then returned directly) and with none of them unresolved (in which case, if the function is pure,
     *                          it is computed and a dummy no-arg function returning the result is returned).
     * @return a function corresponding to the partial application of this function to the parameters of
     * {@code partialParameters} that are not {@link #UNRESOLVED}.
     */
    public default ScalarFunction partialApplication(ProtocolVersion protocolVersion, List<ByteBuffer> partialParameters)
    {
        int unresolvedCount = 0;
        for (ByteBuffer parameter : partialParameters)
        {
            if (parameter == UNRESOLVED)
                ++unresolvedCount;
        }

        if (unresolvedCount == argTypes().size())
            return this;

        if (isPure() && unresolvedCount == 0)
            return new PreComputedScalarFunction(returnType(),
                                           execute(protocolVersion, partialParameters),
                                           protocolVersion,
                                           this,
                                           partialParameters);

        return new PartiallyAppliedScalarFunction(this, partialParameters, unresolvedCount);
    }
}