core/Lucy/Util/Stepper.cfh

/* 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.
 */

parcel Lucy;

/**
 * Abstract encoder/decoder.
 *
 * Many Lucy files consist of a single variable length record type
 * repeated over and over.  A Stepper both reads and writes such a file.
 *
 * Since the write algorithms for different Stepper types may require
 * differing argument lists, it is left to the subclass to define the routine.
 *
 * Sometimes it is possible to change a file's format by changing only a
 * Stepper.  In that case, a compatibility version of the old class may be
 * squirreled away as a plugin, to be accessed only when reading files written
 * to the old format.  This cuts down on special-case code in the most current
 * version.
 *
 * Furthermore, isolating I/O code within a Stepper typically clarifies the
 * logic of the class which calls Stepper_Read_Record.
 */

class Lucy::Util::Stepper inherits Lucy::Object::Obj {

    inert Stepper*
    init(Stepper *self);

    public abstract void
    Reset(Stepper* self);

    /** Update internal state to reflect <code>value</code> and write a frame
     * to <code>outstream</code> that can be read using Read_Key_Frame().
     *
     * @param outstream An OutStream.
     * @param value State information.
     */
    public abstract void
    Write_Key_Frame(Stepper *self, OutStream *outstream, Obj *value);

    /** Update internal state to reflect <code>value</code> and write a frame
     * to <code>outstream</code> that can be read using Read_Delta().
     *
     * @param outstream An OutStream.
     * @param value State information.
     */
    public abstract void
    Write_Delta(Stepper *self, OutStream *outstream, Obj *value);

    /** Update intern state using information read from <code>instream</code>.
     *
     * @param instream An InStream.
     */
    public abstract void
    Read_Key_Frame(Stepper *self, InStream *instream);

    /** Update state using a combination of information from
     * <code>instream</code> and the current internal state.
     */
    public abstract void
    Read_Delta(Stepper *self, InStream *instream);

    /** Read the next record from the instream, storing state in [self].
     */
    abstract void
    Read_Record(Stepper *self, InStream *instream);
}