001    /*
002     * Copyright 2010-2013 JetBrains s.r.o.
003     *
004     * Licensed under the Apache License, Version 2.0 (the "License");
005     * you may not use this file except in compliance with the License.
006     * You may obtain a copy of the License at
007     *
008     * http://www.apache.org/licenses/LICENSE-2.0
009     *
010     * Unless required by applicable law or agreed to in writing, software
011     * distributed under the License is distributed on an "AS IS" BASIS,
012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013     * See the License for the specific language governing permissions and
014     * limitations under the License.
015     */
016    
017    package org.jetbrains.jet.lang.resolve.lazy.storage;
018    
019    import org.jetbrains.annotations.Nullable;
020    import org.jetbrains.jet.utils.WrappedValues;
021    
022    public abstract class NullableLazyValueImpl<T> implements NullableLazyValue<T> {
023        @Nullable
024        private Object value = null;
025    
026        @Override
027        public T compute() {
028            Object _value = value;
029            if (_value != null) return WrappedValues.unescapeNull(_value);
030    
031            T typedValue = doCompute();
032            value = WrappedValues.escapeNull(typedValue);
033    
034            postCompute(typedValue);
035    
036            return typedValue;
037        }
038    
039        protected abstract T doCompute();
040    
041        protected void postCompute(T value) {
042            // Doing something in post-compute helps prevent infinite recursion
043        }
044    }