| 1 | /* |
| 2 | * $Id: ChainFunction.java 562 2010-11-11 00:28:13Z PSpeed $ |
| 3 | * |
| 4 | * The Filament BSD license. |
| 5 | * |
| 6 | * Copyright (c) 2009-2010, the original author or authors |
| 7 | * |
| 8 | * Redistribution and use in source and binary forms, with or without |
| 9 | * modification, are permitted provided that the following conditions |
| 10 | * are met: |
| 11 | * |
| 12 | * 1) Redistributions of source code must retain the above copyright notice, |
| 13 | * this list of conditions and the following disclaimer. |
| 14 | * 2) Redistributions in binary form must reproduce the above copyright |
| 15 | * notice, this list of conditions and the following disclaimer in the |
| 16 | * documentation and/or other materials provided with the distribution. |
| 17 | * 3) Neither the names "Filament", "fgraph.org", "filamentgraph.org", nor the |
| 18 | * names of its contributors may be used to endorse or promote products |
| 19 | * derived from this software without specific prior written permission. |
| 20 | * |
| 21 | * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" |
| 22 | * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| 23 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| 24 | * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE |
| 25 | * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
| 26 | * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
| 27 | * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
| 28 | * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
| 29 | * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| 30 | * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| 31 | * POSSIBILITY OF SUCH DAMAGE. |
| 32 | */ |
| 33 | |
| 34 | package org.fgraph.steps; |
| 35 | |
| 36 | import java.io.Serializable; |
| 37 | |
| 38 | import com.google.common.base.Function; |
| 39 | import com.google.common.collect.Iterables; |
| 40 | |
| 41 | |
| 42 | /** |
| 43 | * Chains the output of one StepFunction to the input |
| 44 | * of another. |
| 45 | * |
| 46 | * @version $Revision: 562 $ |
| 47 | * @author Paul Speed |
| 48 | */ |
| 49 | public class ChainFunction<A, B, C> implements StepFunction<A,C>, Serializable |
| 50 | { |
| 51 | static final long serialVersionUID = 1L; |
| 52 | |
| 53 | // Note for future explorers: |
| 54 | // I'm not sure that <A,? extends B> -> <B,C> |
| 55 | // is materially different than <A,B> -> <? super B,C> |
| 56 | // I can't think of use-cases right now that illustrate |
| 57 | // which one might be better so I'm opting for the |
| 58 | // guava/GCL convention. Given that this is normally |
| 59 | // resolved by the factory method, I'm not sure it matters |
| 60 | // either... since B can be anything and is never exposed |
| 61 | // to the 'user' of the returned Function. |
| 62 | private Function<A,? extends Iterable<? extends B>> f1; |
| 63 | private Function<B,? extends Iterable<C>> f2; |
| 64 | |
| 65 | /** |
| 66 | * Creates a function that feeds the results of the first |
| 67 | * function into the second function and provides a single concatenated |
| 68 | * iterable over those results. |
| 69 | */ |
| 70 | public ChainFunction( Function<A,? extends Iterable<? extends B>> f1, |
| 71 | Function<B,? extends Iterable<C>> f2 ) |
| 72 | { |
| 73 | if( f1 == null || f2 == null ) |
| 74 | throw new IllegalArgumentException( "Supplied functions cannot be null." ); |
| 75 | |
| 76 | this.f1 = f1; |
| 77 | this.f2 = f2; |
| 78 | } |
| 79 | |
| 80 | /** |
| 81 | * Returns an iterable that chains the two chained functions |
| 82 | * together. It does this by getting the result Iterable<B> by |
| 83 | * applying function 1 to the supplied start. Each of the |
| 84 | * results in this iterator is fed through function two and |
| 85 | * all of the Iterable<C>s are concatenated together. This |
| 86 | * is all done lazily on-demand. |
| 87 | */ |
| 88 | public Iterable<C> apply( A start ) |
| 89 | { |
| 90 | Iterable<? extends B> result1 = f1.apply(start); |
| 91 | |
| 92 | // A powerful set of commands. |
| 93 | // It runs f2 on every result of f1 which produces an iterable |
| 94 | // of iterables. Then concat mashes them back together again. |
| 95 | // ...and all of this is evaluated lazily. |
| 96 | return Iterables.concat( Iterables.transform( result1, f2 ) ); |
| 97 | } |
| 98 | |
| 99 | /** |
| 100 | * {@inheritDoc} |
| 101 | */ |
| 102 | public String toString() |
| 103 | { |
| 104 | return "ChainFunction[" + f1 + " -> " + f2 + "]"; |
| 105 | } |
| 106 | } |