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FlatMap.java
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52 lines (44 loc) · 1.62 KB
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/*
* Copyright (c) 2020, Fernando Miguel Carvalho, mcarvalho@cc.isel.ipl.pt
*
* 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 org.jayield.ops;
import org.jayield.Advancer;
import org.jayield.Query;
import org.jayield.Traverser;
import org.jayield.Yield;
import java.util.function.Function;
public class FlatMap<T, R> implements Advancer<R>, Traverser<R> {
private final Query<T> upstream;
private final Function<? super T, ? extends Query<? extends R>> mapper;
private Query<? extends R> src;
public FlatMap(Query<T> query, Function<? super T, ? extends Query<? extends R>> mapper) {
this.upstream = query;
this.mapper = mapper;
src = new Query<>(Advancer.empty(), Traverser.empty());
}
@Override
public void traverse(Yield<? super R> yield) {
upstream.traverse(elem ->
mapper.apply(elem).traverse(yield));
}
@Override
public boolean tryAdvance(Yield<? super R> yield) {
while (!src.tryAdvance(yield)) {
if(!upstream.tryAdvance(t -> src = mapper.apply(t)))
return false;
}
return true;
}
}