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package bjc.utils.funcutils;
import java.util.*;
import java.util.function.*;
import bjc.data.*;
/**
* Utility methods for dealing with iterators.
*
* @author bjculkin
*
*/
public class IteratorUtils {
/**
* Convert an iterator to an iterable.
*
* @param <E> The type being iterated over.
*
* @param itr
* The iterator to convert.
*
* @return An iterable that gives back that iterator.
*/
public static <E> Iterable<E> I(Iterator<E> itr) {
return () -> itr;
}
/**
* Convert an iterable to an iterator.
*
* @param <E> The type being iterated over.
*
* @param itr
* The iterable to convert.
*
* @return The iterator from that iterable
*/
public static <E> Iterator<E> I(Iterable<E> itr) {
return itr.iterator();
}
/**
* Convert an array to an iterator.
*
* @param <E> The type being iterated over.
*
* @param parms
* The array to iterate over.
*
* @return An iterator over the provided array.
*/
@SafeVarargs
public static <E> Iterator<E> I(E... parms) {
return new ArrayIterator<>(parms);
}
/**
* Create a chain iterator.
*
* @param <A> The initial type being iterated over.
* @param <B> The resulting type being iterated over.
*
* @param itrA
* The iterator for input values.
*
* @param itrB
* The transformation for output values.
*
* @return A chain iterator from the provided values.
*/
public static <A, B> Iterator<B> chain(Iterator<A> itrA,
Function<A, Iterator<B>> itrB) {
return new ChainIterator<>(itrA, itrB);
}
/**
* Perform a left-fold over an iterator.
*
* @param <ElementType> The type of elements in the iterator.
* @param <ResultType> The result from the fold.
*
* @param itr The items to iterate over.
* @param zero The initial element for the fold.
* @param folder The function that does the folding.
*
* @return The result of folding over the iterator.
*/
public static <ElementType, ResultType> ResultType foldLeft(
Iterable<ElementType> itr,
ResultType zero,
BiFunction<ElementType, ResultType, ResultType> folder)
{
ResultType state = zero;
for (ElementType elem : itr) {
state = folder.apply(elem, state);
}
return state;
}
/**
* Creates an 'entangled' pair of a consumer and an iterator.
*
* @param <ElementType> The type of value involved.
*
* @return A pair consisting of a consumer of values, and an iterator that
* yields the consumed values.
*/
public static <ElementType>
Pair<Consumer<ElementType>, Iterator<ElementType>> entangle()
{
Queue<ElementType> backer = new ArrayDeque<>();
return Pair.pair(backer::add, new QueueBackedIterator<>(backer));
}
}
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