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/**
* Copyright (c) Rich Hickey. All rights reserved.
* The use and distribution terms for this software are covered by the
* Common Public License 1.0 (http://opensource.org/licenses/cpl.php)
* which can be found in the file CPL.TXT at the root of this distribution.
* By using this software in any fashion, you are agreeing to be bound by
* the terms of this license.
* You must not remove this notice, or any other, from this software.
**/
package clojure.lang;
import java.util.Iterator;
/**
* Implementation of persistent map on a linked list
* Uses identity (==) comparison, vs equals() of PersistentListMap
* Note that instances of this class are constant values
* i.e. add/remove etc return new values
*
* Lookups/changes are linear, so only appropriate for _very_small_ maps
* PersistentArrayMap is generally faster, but this class avoids the double allocation,
* and so is better/faster as a bucket for hash tables
*
* null keys and values are ok, but you won't be able to distinguish a null value via get - use contains/find
*
* code duplication here is kind of gross, but most efficient
*/
public class PersistentListIdentityMap implements IPersistentMap, IMapEntry, ISeq, ISequential
{
static public PersistentListIdentityMap EMPTY = new PersistentListIdentityMap();
static public PersistentListIdentityMap create(Object key, Object val){
return new Tail(key, val);
}
public Object key(){
return null;
}
public Object val(){
return null;
}
PersistentListIdentityMap next(){
return this;
}
public int count(){
return 0;
}
public boolean contains(Object key){
return false;
}
public IMapEntry find(Object key){
return null;
}
public IPersistentMap add(Object key, Object val) throws Exception {
return put(key, val);
}
public PersistentListIdentityMap put(Object key, Object val){
return new Tail(key, val);
}
public PersistentListIdentityMap remove(Object key){
return this;
}
public Object get(Object key){
return null;
}
public int capacity(){
return 0;
}
public Object first() {
return null;
}
public ISeq rest() {
return null;
}
public ISeq seq() {
return null;
}
static class Iter implements Iterator{
PersistentListIdentityMap e;
Iter(PersistentListIdentityMap e)
{
this.e = e;
}
public boolean hasNext(){
return e != EMPTY;
}
public Object next(){
PersistentListIdentityMap ret = e;
e = e.next();
return ret;
}
public void remove(){
throw new UnsupportedOperationException();
}
}
public Iterator iterator(){
return new Iter(this);
}
static class Tail extends PersistentListIdentityMap {
final Object _key;
final Object _val;
Tail(Object key,Object val){
this._key = key;
this._val = val;
}
PersistentListIdentityMap next(){
return EMPTY;
}
public int count(){
return 1;
}
public Object get(Object key){
if(key ==_key)
return _val;
return null;
}
public int capacity(){
return 1;
}
public Object key(){
return _key;
}
public Object val(){
return _val;
}
public boolean contains(Object key){
return key ==_key;
}
public IMapEntry find(Object key){
if(key ==_key)
return this;
return null;
}
public PersistentListIdentityMap add(Object key, Object val) throws Exception{
if(key == _key)
{
throw new Exception("Key already present");
}
return new Link(key,val,this);
}
public PersistentListIdentityMap put(Object key, Object val){
if(key == _key) //replace
{
if(val == _val)
return this;
return new Tail(key,val);
}
return new Link(key,val,this);
}
public PersistentListIdentityMap remove(Object key){
if(key == _key)
return EMPTY;
return this;
}
public Object first() {
return this;
}
public ISeq rest() {
return null;
}
public ISeq seq() {
return this;
}
}
static class Link extends PersistentListIdentityMap {
final Object _key;
final Object _val;
final PersistentListIdentityMap _rest;
Link(Object key,Object val,PersistentListIdentityMap next){
this._key = key;
this._val = val;
this._rest = next;
}
public Object key(){
return _key;
}
public Object val(){
return _val;
}
PersistentListIdentityMap next(){
return _rest;
}
public int count(){
return 1 + _rest.count();
}
public boolean contains(Object key){
return find(key) != null;
}
public IMapEntry find(Object key){
if(key ==_key)
return this;
return _rest.find(key);
}
public PersistentListIdentityMap add(Object key, Object val) throws Exception{
IMapEntry e = find(key);
if(e != null)
{
throw new Exception("Key already present");
}
return new Link(key,val,this);
}
public PersistentListIdentityMap put(Object key, Object val){
IMapEntry e = find(key);
if(e != null)
{
if(e.val() == val)
return this;
return create(_key,_val,remove(key));
}
return new Link(key,val,this);
}
public PersistentListIdentityMap remove(Object key){
if(key == _key)
return _rest;
PersistentListIdentityMap r = _rest.remove(key);
if(r == _rest) //not there
return this;
return create(_key,_val,r);
}
public Object get(Object key){
IMapEntry e = find(key);
if(e != null)
return e.val();
return null;
}
public int capacity(){
return count();
}
public Object first() {
return this;
}
public ISeq rest() {
return _rest;
}
public ISeq seq() {
return this;
}
PersistentListIdentityMap create(Object k,Object v,PersistentListIdentityMap r){
if(r == EMPTY)
return new Tail(k,v);
return new Link(k, v, r);
}
}
}
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