001/*
002 * Copyright (c) 2007-2016 Concurrent, Inc. All Rights Reserved.
003 *
004 * Project and contact information: http://www.cascading.org/
005 *
006 * This file is part of the Cascading project.
007 *
008 * Licensed under the Apache License, Version 2.0 (the "License");
009 * you may not use this file except in compliance with the License.
010 * You may obtain a copy of the License at
011 *
012 *     http://www.apache.org/licenses/LICENSE-2.0
013 *
014 * Unless required by applicable law or agreed to in writing, software
015 * distributed under the License is distributed on an "AS IS" BASIS,
016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
017 * See the License for the specific language governing permissions and
018 * limitations under the License.
019 */
020
021package cascading.tuple.type;
022
023import java.io.Serializable;
024import java.lang.reflect.Type;
025
026/**
027 * Interface CoercibleType allows {@link cascading.tuple.Fields} instances to be extended with custom
028 * type information.
029 * <p/>
030 * It is the role of implementations of this interface to maintain a canonical representation of a given value
031 * and to allow for coercions between some type representation to the canonical type and back.
032 * <p/>
033 * For example, if a field in a text delimited file is a date, ie. {@code 28/Dec/2012:16:17:12:931 -0800}
034 * it may be beneficial for the internal representation to be a {@link Long} value for performance reasons.
035 * <p/>
036 * Note CoercibleType used in conjunction with the TextDelimited parsers is not a replacement for using
037 * a pipe assembly to cleanse data. Pushing data cleansing down to a {@link cascading.tap.Tap} and
038 * {@link cascading.scheme.Scheme} may not provide the flexibility and robustness expected.
039 * <p/>
040 * CoercibleTypes are a convenience when the input data is of high quality or was previously written out using
041 * a CoercibleType instance.
042 * <p/>
043 * The CoercibleTypes further allow the Cascading planner to perform type checks during joins. If no
044 * {@link java.util.Comparator} is in use, and lhs and rhs fields are not the same type, the planner will throw an
045 * exception.
046 */
047public interface CoercibleType<Canonical> extends Type, Serializable
048  {
049  /** @return the actual Java type this CoercibleType represents */
050  Class<Canonical> getCanonicalType();
051
052  /**
053   * @param value of type Object
054   * @return the value coerced into its canonical type
055   */
056  Canonical canonical( Object value );
057
058  /**
059   * @param value of type Object
060   * @param to    of type Type
061   * @return the value coerced into the requested type
062   */
063  <Coerce> Coerce coerce( Object value, Type to );
064  }