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Diffstat (limited to 'sca-cpp/branches/lightweight-sca/modules/java/org/apache/tuscany/IterableUtil.java')
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1 files changed, 398 insertions, 0 deletions
diff --git a/sca-cpp/branches/lightweight-sca/modules/java/org/apache/tuscany/IterableUtil.java b/sca-cpp/branches/lightweight-sca/modules/java/org/apache/tuscany/IterableUtil.java new file mode 100644 index 0000000000..2366d79af6 --- /dev/null +++ b/sca-cpp/branches/lightweight-sca/modules/java/org/apache/tuscany/IterableUtil.java @@ -0,0 +1,398 @@ +/* + * 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.tuscany; + +import static java.util.Arrays.*; + +import java.util.AbstractList; +import java.util.ArrayList; +import java.util.Arrays; +import java.util.Collection; +import java.util.Iterator; +import java.util.List; + +/** + * Utility functions to help work efficiently with iterable lists, inspired from Lisp. + */ +public class IterableUtil { + + /** + * Convert an array or a variable list of arguments to an iterable list. + */ + public static <T> Iterable<T> list(final Object... a) { + return new ArrayIterable<T>(a, 0); + } + + /** + * Convert an iterable list to a java.util.Collection. + */ + @SuppressWarnings("unchecked") + public static <T> Collection<T> collection(final Object l) { + final Collection<T> c = new ArrayList<T>(); + for(final Object x : (Iterable<?>)l) + c.add((T)x); + return c; + } + + /** + * Construct a new list from an element and a list. + */ + public static <T> Iterable<T> cons(final Object car, final Iterable<?> cdr) { + return new PairIterable<T>(car, cdr); + } + + /** + * Return true if a list is nil (empty). + */ + public static boolean isNil(final Object l) { + if(l instanceof BasicIterable<?>) + return ((BasicIterable<?>)l).isNil(); + if(l instanceof Collection<?>) + return ((Collection<?>)l).isEmpty(); + return !((Iterable<?>)l).iterator().hasNext(); + } + + /** + * Return the car (first element) of a list. + */ + @SuppressWarnings("unchecked") + public static <T> T car(final Object l) { + if(l instanceof BasicIterable<?>) + return ((BasicIterable<T>)l).car(); + if(l instanceof List<?>) + return (T)((List<?>)l).get(0); + return (T)((Iterable<?>)l).iterator().next(); + } + + /** + * Return the cdr (rest after the first element) of a list. + */ + @SuppressWarnings("unchecked") + public static <T> Iterable<T> cdr(final Object l) { + if(l instanceof BasicIterable<?>) + return ((BasicIterable<T>)l).cdr(); + if(l instanceof List<?>) + return new ListIterable<T>((List<?>)l, 1); + if(l instanceof Collection<?>) + return new ArrayIterable<T>(((Collection<?>)l).toArray(), 1); + return new Iterable<T>() { + public Iterator<T> iterator() { + final Iterator<T> i = ((Iterable<T>)l).iterator(); + i.next(); + return i; + } + }; + } + + /** + * Return the car of the cdr of a list. + */ + @SuppressWarnings("unchecked") + public static <T> T cadr(final Object l) { + return (T)car(cdr(l)); + } + + /** + * Return the cdr of the cdr of a list. + */ + public static <T> Iterable<T> cddr(final Object l) { + return cdr(cdr(l)); + } + + /** + * Return the cdr of the cdr of the cdr of a list. + */ + public static <T> Iterable<T> cdddr(final Object l) { + return cdr(cdr(cdr(l))); + } + + /** + * Return the car of the cdr of the cdr of a list. + */ + @SuppressWarnings("unchecked") + public static <T> T caddr(final Object l) { + return (T)car(cddr(l)); + } + + /** + * Return the car of the cdr of the cdr of the cdr of a list. + */ + @SuppressWarnings("unchecked") + public static <T> T cadddr(final Object l) { + return (T)car(cdddr(l)); + } + + /** + * Appends a list and another list. + */ + @SuppressWarnings("unchecked") + public static <T> Iterable<T> append(final Object a, final Object b) { + if (isNil(a)) + return (Iterable<T>)b; + return cons(car(a), append(cdr(a), b)); + } + + /** + * Return the first pair matching a key from a list of key value pairs. + */ + public static <T> Iterable<T> assoc(final Object k, final Object l) { + if(isNil(l)) + return list(); + if(k.equals(car(car(l)))) + return car(l); + return assoc(k, cdr(l)); + } + + /** + * Internal base implementation class for iterable and immutable lists. + */ + static abstract class BasicIterable<T> extends AbstractList<T> { + abstract T car(); + + abstract Iterable<T> cdr(); + + abstract Boolean isNil(); + + @Override + public int size() { + return this.isNil()? 0 : 1 + ((List<T>)this.cdr()).size(); + } + + @Override + public T get(final int index) { + throw new UnsupportedOperationException(); + } + } + + /** + * Internal implementation of a list backed by an array. + */ + static class ArrayIterable<T> extends BasicIterable<T> { + final Object[] a; + final int start; + + ArrayIterable(final Object[] a, final int start) { + this.a = a; + this.start = start; + } + + @Override + Boolean isNil() { + return this.a.length - this.start == 0; + } + + @SuppressWarnings("unchecked") + @Override + T car() { + return (T)this.a[this.start]; + } + + @Override + BasicIterable<T> cdr() { + return new ArrayIterable<T>(this.a, this.start + 1); + } + + @Override + public Iterator<T> iterator() { + return new Iterator<T>() { + int i = ArrayIterable.this.start; + + public boolean hasNext() { + return this.i < ArrayIterable.this.a.length; + } + + @SuppressWarnings("unchecked") + public T next() { + return (T)ArrayIterable.this.a[this.i++]; + } + + public void remove() { + throw new UnsupportedOperationException(); + } + }; + } + } + + /** + * Internal implementation of a list backed by a java.util.List. + */ + static class ListIterable<T> extends BasicIterable<T> { + final List<?> l; + final int start; + + ListIterable(final List<?> l, final int start) { + this.l = l; + this.start = start; + } + + @Override + Boolean isNil() { + return this.l.size() - this.start == 0; + } + + @SuppressWarnings("unchecked") + @Override + T car() { + return (T)this.l.get(this.start); + } + + @Override + BasicIterable<T> cdr() { + return new ListIterable<T>(this.l, this.start + 1); + } + + @Override + public Iterator<T> iterator() { + return new Iterator<T>() { + int i = ListIterable.this.start; + + public boolean hasNext() { + return this.i < ListIterable.this.l.size(); + } + + @SuppressWarnings("unchecked") + public T next() { + return (T)ListIterable.this.l.get(this.i++); + } + + public void remove() { + throw new UnsupportedOperationException(); + } + }; + } + } + + /** + * Internal implementation of a list backed by an element / iterable pair. + */ + static class PairIterable<T> extends BasicIterable<T> { + final Object car; + final Iterable<?> cdr; + + PairIterable(final Object car, final Iterable<?> cdr) { + this.car = car; + this.cdr = cdr; + } + + @Override + Boolean isNil() { + return false; + } + + @SuppressWarnings("unchecked") + @Override + T car() { + return (T)this.car; + } + + @SuppressWarnings("unchecked") + @Override + Iterable<T> cdr() { + return (Iterable<T>)this.cdr; + } + + @Override + public Iterator<T> iterator() { + return new Iterator<T>() { + boolean carIterator = true; + Iterator<?> cdrIterator = PairIterable.this.cdr.iterator(); + + public boolean hasNext() { + if(this.carIterator) + return true; + return this.cdrIterator.hasNext(); + } + + @SuppressWarnings("unchecked") + public T next() { + if(this.carIterator) { + this.carIterator = false; + return (T)PairIterable.this.car; + } + return (T)this.cdrIterator.next(); + } + + public void remove() { + throw new UnsupportedOperationException(); + } + }; + } + } + + /** + * Test the list functions. + */ + static class Test { + Boolean testList() { + final Iterable<Object> l = list(2, 3, 4); + assert car(l) == Integer.valueOf(2); + assert cadr(l) == Integer.valueOf(3); + assert caddr(l) == Integer.valueOf(4); + + final Iterable<Object> c = cons(0, cons(1, l)); + assert car(c) == Integer.valueOf(0); + assert cadr(c) == Integer.valueOf(1); + assert caddr(c) == Integer.valueOf(2); + assert c.toString().equals("[0, 1, 2, 3, 4]"); + + final Iterable<Object> cl = cons(0, cons(1, new ArrayList<Object>(asList(2, 3, 4)))); + assert car(cl) == Integer.valueOf(0); + assert cadr(cl) == Integer.valueOf(1); + assert caddr(cl) == Integer.valueOf(2); + assert cl.toString().equals("[0, 1, 2, 3, 4]"); + + final List<Object> jl = new ArrayList<Object>(collection(cl)); + assert jl.size() == 5; + assert jl.get(0) == Integer.valueOf(0); + assert jl.get(1) == Integer.valueOf(1); + assert jl.get(2) == Integer.valueOf(2); + + final Iterable<Object> n = list(); + assert isNil(n); + assert n.toString().equals("[]"); + + final Iterable<Object> cn = cons(0, n); + assert !isNil(cn); + assert isNil(cdr(cn)); + assert cn.toString().equals("[0]"); + + final Iterable<Object> al = new ArrayList<Object>(Arrays.asList(1, 2, 3)); + assert car(al) == Integer.valueOf(1); + assert cadr(al) == Integer.valueOf(2); + assert caddr(al) == Integer.valueOf(3); + + final Iterable<Object> a = list(0, 1, 2); + final Iterable<Object> b = list(3, 4); + final Iterable<Object> ab = append(a, b); + assert ab.toString().equals("[0, 1, 2, 3, 4]"); + return true; + } + } + + public static void main(final String[] args) { + System.out.println("Testing..."); + + Test.class.getClassLoader().setDefaultAssertionStatus(true); + new Test().testList(); + + System.out.println("OK"); + } + +} |