com.ajjpj.afoundation.collection.immutable.AList Maven / Gradle / Ivy
package com.ajjpj.afoundation.collection.immutable;
import com.ajjpj.afoundation.collection.ACollectionHelper;
import com.ajjpj.afoundation.collection.AEquality;
import com.ajjpj.afoundation.function.AFunction1;
import com.ajjpj.afoundation.function.APartialFunction;
import com.ajjpj.afoundation.function.APredicate;
import java.io.*;
import java.lang.reflect.Array;
import java.util.*;
/**
* This is an immutable linked list implementation. It provides "mutators" that return copies of the list without
* affecting the original ("copy on write").
*
* The API is based on terminology of functional languages. NIL is the empty list, head is the list's
* first element, tail is the list without its first element, and cons() is the
* operation that prepends an element to an existing list.
*
* @author arno
*/
abstract public class AList extends AbstractACollection> implements Serializable {
private final int size;
protected AList(int size) {
this.size = size;
}
/**
* Returns the empty list. All calls to this method are guaranteed to return the same instance.
*/
@SuppressWarnings("unchecked")
public static AList nil() {
return (AList) Nil.INSTANCE;
}
public static final AList nil = Nil.INSTANCE;
/**
* Creates an AList based on the contents of an existing java.util.Iterable, copying its contents.
*/
public static AList create(Iterable elements) {
if (elements instanceof AList) {
return (AList) elements;
}
if(elements instanceof List) {
return create((List) elements);
}
AList result = nil();
for(T el: elements) {
result = result.cons(el);
}
return result.reverse();
}
/**
* Creates an AList based on the contents of an existing java.util.List, copying its content.
*/
public static AList create(List elements) {
AList result = nil();
for(int i=elements.size()-1; i>=0; i--) {
result = result.cons(elements.get(i));
}
return result;
}
/**
* Creates an AList from a given list of elements.
*/
@SafeVarargs
public static AList create(T... elements) {
return create(Arrays.asList(elements));
}
/**
* Returns a read-only java.util.List view of this AList.
*/
public java.util.List asJavaUtilList() {
return new JuListWrapper<>(this);
}
@Override public Collection asJavaUtilCollection () {
return asJavaUtilList ();
}
@Override protected AList createInternal(Collection elements) {
return AList.create (elements);
}
@Override protected AEquality equalityForEquals() {
return AEquality.EQUALS;
}
/**
* Returns this AList's head, if any.
*/
public abstract AOption optHead();
/**
* Returns the list's head, i.e. its first element. If called on the empty list, it throws a NoSuchElementException.
*/
public abstract T head();
/**
* Returns the list's tail, i.e. the list without its first element. If called on the empty list, it throws a
* NoSuchElementException.
*/
public abstract AList tail();
/**
* Returns a new AList with the new element prepended. This is the only operation to 'add' elements to an AList.
*/
public AList cons(T el) {
return new AHead<>(el, this);
}
/**
* Returns a copy of this AList with elements in reversed order.
*/
public AList reverse() {
AList remaining = this;
AList result = nil();
while(! remaining.isEmpty()) {
result = result.cons(remaining.head());
remaining = remaining.tail();
}
return result;
}
public int size() {
return size;
}
@Override public AList toList() {
// override as an optimization
return this;
}
@Override public AList map (AFunction1 f) throws E {
return create(ACollectionHelper.map(this, f));
}
@Override public AList flatMap(AFunction1, E> f) throws E {
return create(ACollectionHelper.flatMap (this, f));
}
@SuppressWarnings("unchecked")
@Override public AList flatten() {
return (AList) create(ACollectionHelper.flatten((Iterable>) this));
}
@Override public AList collect (APartialFunction pf) throws E {
return create (ACollectionHelper.collect (this, pf));
}
/**
* Returns a java.util.Iterator over this AList's elements, allowing ALists to be used with Java's
* for(...: list) syntax introduced in version 1.5.
*/
@Override
public Iterator iterator() {
return new Iterator() {
AList pos = AList.this;
@Override
public boolean hasNext() {
return pos.nonEmpty();
}
@Override
public T next() {
final T result = pos.head();
pos = pos.tail();
return result;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
static final class AHead extends AList {
private final T head;
private final AList tail;
AHead(T head, AList tail) {
super(tail.size() + 1);
this.head = head;
this.tail = tail;
}
@Override public AOption optHead() {
return AOption.some(head);
}
@Override public T head() {
return head;
}
@Override public AList tail() {
return tail;
}
@Override public boolean contains (T el) {
return AEquality.EQUALS.equals (el, head) || tail.contains (el);
}
@Override public ACollection clear () {
return nil;
}
}
static final class Nil extends AList