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Library providing immutable/persistent collection classes for
Java. While collections are immutable they provide methods for
adding and removing values by creating new modified copies of
themselves. Each copy shares almost all of its structure with
other copies to minimize memory consumption.
///###////////////////////////////////////////////////////////////////////////
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// Burton Computer Corporation
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// Copyright (c) 2019, Burton Computer Corporation
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package org.javimmutable.collections.util;
import org.javimmutable.collections.Func1;
import org.javimmutable.collections.Func2;
import org.javimmutable.collections.Holder;
import org.javimmutable.collections.Holders;
import org.javimmutable.collections.Insertable;
import org.javimmutable.collections.JImmutableMap;
import org.javimmutable.collections.list.JImmutableLinkedStack;
import java.util.Iterator;
import java.util.Map;
/**
* Library of static functions that perform various operations on Iterators.
*/
public final class Functions
{
private Functions()
{
}
/**
* Calls func for every value in iterator passing in the accumulator and each value as parameters
* and setting accumulator to the result. The final accumulator value is returned.
*/
public static R foldLeft(R accumulator,
Iterator iterator,
Func2 func)
{
while (iterator.hasNext()) {
accumulator = func.apply(accumulator, iterator.next());
}
return accumulator;
}
/**
* Calls func for every value in iterator from right to left (i.e. in reverse order) passing in the accumulator and each value
* as parameters and setting the accumulator to the result. The final accumulator value is returned.
* Requires 2x time compared to foldLeft() since it reverses the order of the iterator before calling the function.
*/
public static R foldRight(R accumulator,
Iterator iterator,
Func2 func)
{
return foldLeft(accumulator, reverse(iterator), func);
}
/**
* Creates a new Iterator whose values are in the reverse order of the provided Iterator.
* Requires O(n) time and creates an intermediate copy of the Iterator's values.
*/
public static Iterator reverse(Iterator iterator)
{
return JImmutableLinkedStack.of().insertAll(iterator).iterator();
}
/**
* Calls func for every value in iterator and adds each value returned by func
* to a list. Returns the resulting list.
*
* @param iterator source of the values
* @param func function to transform the values
* @param list list to receive the values
*/
@SuppressWarnings("unchecked")
public static > A collectAll(Iterator iterator,
A list,
Func1 func)
{
while (iterator.hasNext()) {
list = list.insert(func.apply(iterator.next()));
}
return list;
}
/**
* Calls func for every value in iterator and adds each value for which func returns a non-empty
* Holder to a list. Returns the resulting list.
*
* @param iterator source of the values
* @param func function to reject the values
* @param list list to receive the values
*/
@SuppressWarnings("unchecked")
public static > A collectSome(Iterator iterator,
A list,
Func1> func)
{
while (iterator.hasNext()) {
Holder mappedValue = func.apply(iterator.next());
if (mappedValue.isFilled()) {
list = list.insert(mappedValue.getValue());
}
}
return list;
}
/**
* Calls func for each value in iterator and passes it to func until func returns true.
* If func returns true the value is returned. If func never returns true an empty
* value is returned.
*/
public static Holder find(Iterator iterator,
Func1 func)
{
while (iterator.hasNext()) {
final T value = iterator.next();
if (func.apply(value)) {
return Holders.of(value);
}
}
return Holders.of();
}
/**
* Calls func for every value in iterator and adds each value for which func returns false
* to a list. Returns the resulting list.
*
* @param iterator source of the values
* @param func function to reject the values
* @param list list to receive the values
*/
@SuppressWarnings("unchecked")
public static > A reject(Iterator iterator,
A list,
Func1 func)
{
while (iterator.hasNext()) {
final T value = iterator.next();
if (!func.apply(value)) {
list = list.insert(value);
}
}
return list;
}
/**
* Calls func for every value in iterator and adds each value for which func returns true
* to a list. Returns the resulting list.
*
* @param iterator source of the values
* @param func function to select the values
* @param list list to receive the values
*/
@SuppressWarnings("unchecked")
public static > A select(Iterator iterator,
A list,
Func1 func)
{
while (iterator.hasNext()) {
final T value = iterator.next();
if (func.apply(value)) {
list = list.insert(value);
}
}
return list;
}
public static JImmutableMap assignAll(JImmutableMap dest,
JImmutableMap src)
{
for (JImmutableMap.Entry entry : src) {
dest = dest.assign(entry.getKey(), entry.getValue());
}
return dest;
}
public static JImmutableMap assignAll(JImmutableMap dest,
Map src)
{
for (Map.Entry entry : src.entrySet()) {
dest = dest.assign(entry.getKey(), entry.getValue());
}
return dest;
}
}