Refactoring select, reject, and reduce to use Iterables instead of Cursorables.

Author: brianburton

src/main/java/org/javimmutable/collections/Cursorable.java

@@ -36,7 +36,6 @@
 package org.javimmutable.collections;
 
 import javax.annotation.Nonnull;
-import java.util.function.BiFunction;
 
 /**
  * Implemented by objects that can create a Cursor for a given type.
@@ -46,14 +45,4 @@ public interface Cursorable<T>
 {
     @Nonnull
     Cursor<T> cursor();
-
-    default <R> R reduce(R initialValue,
-                         @Nonnull BiFunction<R, T, R> operator)
-    {
-        R result = initialValue;
-        for (Cursor<T> cursor = cursor().start(); cursor.hasValue(); cursor = cursor.next()) {
-            result = operator.apply(result, cursor.getValue());
-        }
-        return result;
-    }
 }

src/main/java/org/javimmutable/collections/JImmutableList.java

@@ -258,8 +258,7 @@ JImmutableList<T> assign(int index,
     default JImmutableList<T> select(@Nonnull Predicate<T> predicate)
     {
         JImmutableList<T> answer = deleteAll();
-        for (Cursor<T> cursor = cursor().start(); cursor.hasValue(); cursor = cursor.next()) {
-            final T value = cursor.getValue();
+        for (T value : this) {
             if (predicate.test(value)) {
                 answer = answer.insert(value);
             }

src/main/java/org/javimmutable/collections/JImmutableRandomAccessList.java

@@ -45,25 +45,20 @@
 /**
  * Extension of JImmutableList that allows insertion and deletion at arbitrary
  * indexes within the list.
- *
- * @param <T>
  */
 @Immutable
 public interface JImmutableRandomAccessList<T>
-        extends JImmutableList<T>
+    extends JImmutableList<T>
 {
     interface Builder<T>
-            extends MutableBuilder<T, JImmutableRandomAccessList<T>>
+        extends MutableBuilder<T, JImmutableRandomAccessList<T>>
     {
     }
 
     /**
      * Replaces the value at the specified index (which must be within current
      * bounds of the list) with the new value.
      *
-     * @param index
-     * @param value
-     * @return
      * @throws IndexOutOfBoundsException if index is out of bounds
      */
     @Nonnull
@@ -72,9 +67,6 @@ JImmutableRandomAccessList<T> assign(int index,
 
     /**
      * Adds a value to the end of the list.  May be invoked on an empty list.
-     *
-     * @param value
-     * @return
      */
     @Nonnull
     JImmutableRandomAccessList<T> insert(@Nullable T value);
@@ -83,10 +75,6 @@ JImmutableRandomAccessList<T> assign(int index,
      * Insert value at index (which must be within 0 to size).
      * Shifts all values at and after index one position to the right and adds 1
      * to size of the list.
-     *
-     * @param index
-     * @param value
-     * @return
      */
     @Nonnull
     JImmutableRandomAccessList<T> insert(int index,
@@ -95,19 +83,13 @@ JImmutableRandomAccessList<T> insert(int index,
     /**
      * Adds a value to the front of the list.  May be invoked on an empty list.
      * Synonym for insert()
-     *
-     * @param value
-     * @return
      */
     @Nonnull
     JImmutableRandomAccessList<T> insertFirst(@Nullable T value);
 
     /**
      * Adds a value to the end of the list.  May be invoked on an empty list.
      * Synonym for insert().
-     *
-     * @param value
-     * @return
      */
     @Nonnull
     JImmutableRandomAccessList<T> insertLast(@Nullable T value);
@@ -116,7 +98,6 @@ JImmutableRandomAccessList<T> insert(int index,
      * Adds the values to the end of the list in the same order they appear in the Iterable.  May be invoked on an empty list.
      * Synonym for insertAllLast()
      *
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -126,7 +107,6 @@ JImmutableRandomAccessList<T> insert(int index,
      * Adds the values to the end of the list in the same order they appear in the Iterable.  May be invoked on an empty list.
      * Synonym for insertAllLast()
      *
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -136,7 +116,6 @@ JImmutableRandomAccessList<T> insert(int index,
      * Adds the values to the end of the list in the same order they appear in the Iterable.  May be invoked on an empty list.
      * Synonym for insertAllLast()
      *
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -146,7 +125,6 @@ JImmutableRandomAccessList<T> insert(int index,
      * Adds the values to the end of the list in the same order they appear in the Iterable.  May be invoked on an empty list.
      * Synonym for insertAllLast()
      *
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -158,8 +136,6 @@ JImmutableRandomAccessList<T> insert(int index,
      * Shifts all values at and after index x positions to the right and adds x
      * to size of the list, where x is the number of elements being inserted.
      *
-     * @param index
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -172,8 +148,6 @@ JImmutableRandomAccessList<T> insertAll(int index,
      * Shifts all values at and after index x positions to the right and adds x
      * to size of the list, where x is the number of elements being inserted.
      *
-     * @param index
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -186,8 +160,6 @@ JImmutableRandomAccessList<T> insertAll(int index,
      * Shifts all values at and after index x positions to the right and adds x
      * to size of the list, where x is the number of elements being inserted.
      *
-     * @param index
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -200,8 +172,6 @@ JImmutableRandomAccessList<T> insertAll(int index,
      * Shifts all values at and after index x positions to the right and adds x
      * to size of the list, where x is the number of elements being inserted.
      *
-     * @param index
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -211,7 +181,6 @@ JImmutableRandomAccessList<T> insertAll(int index,
     /**
      * Adds the values to the beginning of the list in the same order they appear in the Iterable.  May be invoked on an empty list.
      *
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -220,7 +189,6 @@ JImmutableRandomAccessList<T> insertAll(int index,
     /**
      * Adds the values to the beginning of the list in the same order they appear in the Iterable.  May be invoked on an empty list.
      *
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -229,7 +197,6 @@ JImmutableRandomAccessList<T> insertAll(int index,
     /**
      * Adds the values to the beginning of the list in the same order they appear in the Iterable.  May be invoked on an empty list.
      *
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -238,7 +205,6 @@ JImmutableRandomAccessList<T> insertAll(int index,
     /**
      * Adds the values to the beginning of the list in the same order they appear in the Iterable.  May be invoked on an empty list.
      *
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -248,7 +214,6 @@ JImmutableRandomAccessList<T> insertAll(int index,
      * Adds the values to the end of the list in the same order they appear in the Iterable.  May be invoked on an empty list.
      * Synonym for insertAll()
      *
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -258,7 +223,6 @@ JImmutableRandomAccessList<T> insertAll(int index,
      * Adds the values to the end of the list in the same order they appear in the Iterable.  May be invoked on an empty list.
      * Synonym for insertAll()
      *
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -268,7 +232,6 @@ JImmutableRandomAccessList<T> insertAll(int index,
      * Adds the values to the end of the list in the same order they appear in the Iterable.  May be invoked on an empty list.
      * Synonym for insertAll()
      *
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -278,7 +241,6 @@ JImmutableRandomAccessList<T> insertAll(int index,
      * Adds the values to the end of the list in the same order they appear in the Iterable.  May be invoked on an empty list.
      * Synonym for insertAll()
      *
-     * @param values
      * @return instance of list containing the collection
      */
     @Nonnull
@@ -306,9 +268,6 @@ JImmutableRandomAccessList<T> insertAll(int index,
      * Delete value at index (which must be within the current bounds of the list).
      * Shifts all values at and after index one position to the left and subtracts 1
      * from size of the list.
-     *
-     * @param index
-     * @return
      */
     @Nonnull
     JImmutableRandomAccessList<T> delete(int index);
@@ -333,8 +292,7 @@ default JImmutableRandomAccessList<T> reject(@Nonnull Predicate<T> predicate)
     {
         JImmutableRandomAccessList<T> answer = this;
         int index = 0;
-        for (Cursor<T> cursor = cursor().start(); cursor.hasValue(); cursor = cursor.next()) {
-            final T value = cursor.getValue();
+        for (T value : this) {
             assert value == answer.get(index);
             if (predicate.test(value)) {
                 answer = answer.delete(index);

src/main/java/org/javimmutable/collections/SplitableIterable.java

@@ -36,6 +36,7 @@
 package org.javimmutable.collections;
 
 import javax.annotation.Nonnull;
+import java.util.function.BiFunction;
 
 /**
  * Extension of Iterable for objects whose iterator method returns a SplitableIterator.
@@ -46,4 +47,18 @@ public interface SplitableIterable<T>
     @Override
     @Nonnull
     SplitableIterator<T> iterator();
+
+    /**
+     * Default reduce operation.  Can be used without requiring a stream to quickly collect
+     * information from an iterable object in a single thread.
+     */
+    default <R> R reduce(R initialValue,
+                         @Nonnull BiFunction<R, T, R> operator)
+    {
+        R result = initialValue;
+        for (T value : this) {
+            result = operator.apply(result, value);
+        }
+        return result;
+    }
 }

src/test/java/org/javimmutable/collections/cursors/StandardCursorTest.java

@@ -52,7 +52,6 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.NoSuchElementException;
-import java.util.function.BiFunction;
 
 import static java.util.Arrays.asList;
 import static org.assertj.core.api.Assertions.*;
@@ -86,17 +85,6 @@ public static void testVarious()
         listCursorTest(Arrays.asList(1, 2), StandardCursor.of(() -> new StandardCursor.RangeSource(1, 2)));
     }
 
-    public void testReduce()
-    {
-        final Double zero = 0.0;
-        final BiFunction<Double, Integer, Double> operator = (s, v) -> s + ((double)v) / 2.0;
-        assertSame(zero, StandardCursor.<Integer>emptyCursorable().reduce(zero, operator));
-        assertEquals(0.0, rangeCursorable(0, 0).reduce(zero, operator));
-        assertEquals(0.5, rangeCursorable(0, 1).reduce(zero, operator));
-        assertEquals(1.5, rangeCursorable(0, 2).reduce(zero, operator));
-        assertEquals(3.0, rangeCursorable(0, 3).reduce(zero, operator));
-    }
-
     public void testSplitAllowed()
     {
         assertEquals(false, forRange(1, 0).start().isSplitAllowed());

src/test/java/org/javimmutable/collections/iterators/IndexedIteratorTest.java

@@ -36,8 +36,11 @@
 package org.javimmutable.collections.iterators;
 
 import junit.framework.TestCase;
+import org.javimmutable.collections.SplitableIterable;
 import org.javimmutable.collections.indexed.IndexedHelper;
 
+import java.util.function.BiFunction;
+
 import static java.util.Arrays.asList;
 import static org.javimmutable.collections.iterators.StandardIteratorTests.*;
 
@@ -55,4 +58,25 @@ public void test()
         verifyOrderedSplit(true, asList(1), asList(2, 3), IndexedIterator.iterator(IndexedHelper.indexed(1, 2, 3)));
         verifyOrderedSplit(true, asList(1, 2), asList(3, 4, 5), IndexedIterator.forRange(1, 5));
     }
+
+    public void testReduce()
+    {
+        final Double zero = 0.0;
+        final BiFunction<Double, Integer, Double> operator = (s, v) -> s + ((double)v) / 2.0;
+        assertSame(zero, emptyIterable().reduce(zero, operator));
+        assertEquals(0.0, rangeIterable(0).reduce(zero, operator));
+        assertEquals(0.5, rangeIterable(1).reduce(zero, operator));
+        assertEquals(1.5, rangeIterable(2).reduce(zero, operator));
+        assertEquals(3.0, rangeIterable(3).reduce(zero, operator));
+    }
+
+    private SplitableIterable<Integer> emptyIterable()
+    {
+        return () -> EmptyIterator.of();
+    }
+
+    private SplitableIterable<Integer> rangeIterable(int high)
+    {
+        return () -> IndexedIterator.forRange(0, high);
+    }
 }