/*
* Copyright 2003-2014 JetBrains s.r.o.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package jetbrains.mps.util.iterable;
import org.jetbrains.annotations.NotNull;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
/**
* {@link java.lang.Iterable} with filtering capability, each distinct element of initial sequence is reported only once.
* Note, <code>null</code> elements get filtered out and are not reported at all.
* XXX why not ConditionalIterable with appropriate condition (although would need state-aware condition, to reset on each #iterator())
*/
public class DistinctIterator<T> implements Iterable<T>, Iterator<T> {
private final Iterable<T> mySource;
private final Set<T> mySeen = new HashSet<T>();
private T myNext;
private Iterator<T> myCurrent;
public DistinctIterator(@NotNull Iterable<T> inner) {
mySource = inner;
}
protected T nextElement() {
while (myCurrent.hasNext()) {
final T next = myCurrent.next();
if (next != null) {
if (mySeen.add(next)) {
return next;
}
}
}
mySeen.clear();
return null;
}
@Override
public final boolean hasNext() {
return myNext != null;
}
@Override
public final T next() {
final T result = myNext;
myNext = nextElement();
return result;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
@Override
public Iterator<T> iterator() {
mySeen.clear();
myCurrent = mySource.iterator();
myNext = nextElement();
return this;
}
}