| // Copyright 2017 The Bazel Authors. All rights reserved. |
| // |
| // 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 com.google.devtools.build.lib.query2.engine; |
| |
| import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe; |
| |
| /** |
| * Helper for extracting a key of type {@code K} from an element of type {@code T}. |
| * |
| * <p>Depending on the choice of {@code K}, this enables potential memory optimizations. |
| */ |
| @ThreadSafe |
| public interface KeyExtractor<T, K> { |
| /** Extracts an unique key that can be used to dedupe the given {@code element}. */ |
| K extractKey(T element); |
| |
| static <T1, T2, K> KeyExtractor<T1, K> compose( |
| KeyExtractor<T1, ? extends T2> inner, KeyExtractor<T2, K> outer) { |
| return t1 -> outer.extractKey(inner.extractKey(t1)); |
| } |
| } |