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/*
* Copyright (c) 2021 Goldman Sachs.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* and Eclipse Distribution License v. 1.0 which accompany this distribution.
* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
* and the Eclipse Distribution License is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*/
package org.eclipse.collections.impl.utility;
import org.eclipse.collections.api.LazyIterable;
import org.eclipse.collections.api.RichIterable;
import org.eclipse.collections.api.block.function.Function;
import org.eclipse.collections.api.block.function.Function2;
import org.eclipse.collections.api.block.predicate.Predicate;
import org.eclipse.collections.api.block.procedure.Procedure;
import org.eclipse.collections.api.factory.Lists;
import org.eclipse.collections.api.tuple.Pair;
import org.eclipse.collections.impl.lazy.ChunkIterable;
import org.eclipse.collections.impl.lazy.CollectIterable;
import org.eclipse.collections.impl.lazy.CompositeIterable;
import org.eclipse.collections.impl.lazy.DistinctIterable;
import org.eclipse.collections.impl.lazy.DropIterable;
import org.eclipse.collections.impl.lazy.DropWhileIterable;
import org.eclipse.collections.impl.lazy.FlatCollectIterable;
import org.eclipse.collections.impl.lazy.LazyIterableAdapter;
import org.eclipse.collections.impl.lazy.RejectIterable;
import org.eclipse.collections.impl.lazy.SelectInstancesOfIterable;
import org.eclipse.collections.impl.lazy.SelectIterable;
import org.eclipse.collections.impl.lazy.TakeIterable;
import org.eclipse.collections.impl.lazy.TakeWhileIterable;
import org.eclipse.collections.impl.lazy.TapIterable;
import org.eclipse.collections.impl.lazy.ZipIterable;
import org.eclipse.collections.impl.lazy.ZipWithIndexIterable;
import org.eclipse.collections.impl.tuple.Tuples;
/**
* LazyIterate is a factory class which creates "deferred" iterables around the specified iterables. A "deferred"
* iterable performs some operation, such as filtering or transforming, when the result iterable is iterated over. This
* makes the operation very memory efficient, because you don't have to create intermediate collections during the
* operation.
*
* @since 1.0
*/
public final class LazyIterate
{
private static final LazyIterable EMPTY_ITERABLE = Lists.immutable.empty().asLazy();
private LazyIterate()
{
throw new AssertionError("Suppress default constructor for noninstantiability");
}
/**
* Creates a deferred rich iterable for the specified iterable.
*/
public static LazyIterable adapt(Iterable iterable)
{
return new LazyIterableAdapter<>(iterable);
}
/**
* Creates a deferred filtering iterable for the specified iterable.
*/
public static LazyIterable select(Iterable iterable, Predicate predicate)
{
return new SelectIterable<>(iterable, predicate);
}
/**
* Creates a deferred negative filtering iterable for the specified iterable.
*/
public static LazyIterable reject(Iterable iterable, Predicate predicate)
{
return new RejectIterable<>(iterable, predicate);
}
public static LazyIterable selectInstancesOf(Iterable iterable, Class clazz)
{
return new SelectInstancesOfIterable<>(iterable, clazz);
}
/**
* Creates a deferred transforming iterable for the specified iterable.
*/
public static LazyIterable collect(
Iterable iterable,
Function function)
{
return new CollectIterable<>(iterable, function);
}
/**
* Creates a deferred flattening iterable for the specified iterable.
*/
public static LazyIterable flatCollect(
Iterable iterable,
Function> function)
{
return new FlatCollectIterable<>(iterable, function);
}
/**
* Creates a deferred filtering and transforming iterable for the specified iterable.
*/
public static LazyIterable collectIf(
Iterable iterable,
Predicate predicate,
Function function)
{
return LazyIterate.select(iterable, predicate).collect(function);
}
/**
* Creates a deferred take iterable for the specified iterable using the specified count as the limit.
*/
public static LazyIterable take(Iterable iterable, int count)
{
return new TakeIterable<>(iterable, count);
}
/**
* Creates a deferred drop iterable for the specified iterable using the specified count as the size to drop.
*/
public static LazyIterable drop(Iterable iterable, int count)
{
return new DropIterable<>(iterable, count);
}
/**
* Creates a deferred takeWhile iterable for the specified iterable using the specified predicate.
* Short circuits at the first element which does not satisfy the Predicate.
*
* @since 8.0
*/
public static LazyIterable takeWhile(Iterable iterable, Predicate predicate)
{
return new TakeWhileIterable<>(iterable, predicate);
}
/**
* Creates a deferred dropWhile iterable for the specified iterable using the specified count as the size to drop.
* Short circuits at the first element which satisfies the Predicate.
*
* @since 8.0
*/
public static LazyIterable dropWhile(Iterable iterable, Predicate predicate)
{
return new DropWhileIterable<>(iterable, predicate);
}
/**
* Creates a deferred distinct iterable for the specified iterable.
*
* @since 5.0
*/
public static LazyIterable distinct(Iterable iterable)
{
return new DistinctIterable<>(iterable);
}
/**
* Combines iterables into a deferred composite iterable.
*/
public static LazyIterable concatenate(Iterable... iterables)
{
return CompositeIterable.with(iterables);
}
public static LazyIterable empty()
{
return (LazyIterable) EMPTY_ITERABLE;
}
public static LazyIterable> zip(Iterable as, Iterable bs)
{
return new ZipIterable<>(as, bs);
}
public static LazyIterable> zipWithIndex(Iterable iterable)
{
return new ZipWithIndexIterable<>(iterable);
}
public static LazyIterable> chunk(Iterable iterable, int size)
{
return new ChunkIterable<>(iterable, size);
}
/**
* Creates a deferred tap iterable for the specified iterable.
*
* @since 6.0
*/
public static LazyIterable tap(Iterable iterable, Procedure procedure)
{
return new TapIterable<>(iterable, procedure);
}
/**
* Create a deferred cartesian product of the two specified iterables.
*
* See {@link LazyIterate#cartesianProduct(Iterable, Iterable, Function2)} about performance and presence of duplicates.
*
* @since 10.0
*/
public static LazyIterable> cartesianProduct(Iterable iterable1, Iterable iterable2)
{
return LazyIterate.cartesianProduct(iterable1, iterable2, Tuples::pair);
}
/**
* Create a deferred cartesian product of the two specified iterables.
*
* This operation has O(n^2) performance.
*
* The presence of duplicates in the resulting iterable is both dependent on the
* presence of duplicates in the two specified iterables, and on the behaviour
* of the terminating operation that is applied to the resulting lazy iterable.
*
* @since 10.0
*/
public static LazyIterable cartesianProduct(Iterable iterable1, Iterable iterable2, Function2 function)
{
return LazyIterate.flatCollect(iterable1, first -> LazyIterate.collect(iterable2, second -> function.value(first, second)));
}
}