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
017package org.jetbrains.jet.util.lazy;
018
019public abstract class RecursionIntolerantLazyValue<T> {
020
021    private enum State {
022        NOT_COMPUTED,
023        BEING_COMPUTED,
024        COMPUTED,
025        ERROR
026    }
027
028    private State state = State.NOT_COMPUTED;
029    private T value;
030
031    protected abstract T compute();
032
033    protected T getValueOnErrorReentry() {
034        throw new ReenteringLazyValueComputationException();
035    }
036
037    public boolean isComputed() {
038        return state == State.ERROR || state == State.COMPUTED;
039    }
040
041    public final T get() {
042        switch (state) {
043            case NOT_COMPUTED:
044                state = State.BEING_COMPUTED;
045                value = compute();
046                state = State.COMPUTED;
047                return value;
048            case BEING_COMPUTED:
049                state = State.ERROR;
050                throw new ReenteringLazyValueComputationException();
051            case COMPUTED:
052                return value;
053            case ERROR:
054                return getValueOnErrorReentry();
055        }
056        throw new IllegalStateException("Unreachable");
057    }
058
059
060
061}