org.organicdesign.fp.function.Function0 Maven / Gradle / Ivy

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// Copyright 2015-03-06 PlanBase Inc. & Glen Peterson
//
// 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.organicdesign.fp.function;

import java.io.Serializable;
import java.util.concurrent.Callable;
import java.util.function.Supplier;

/**
 This is like Java 8's java.util.function.Supplier, but retrofitted to turn checked exceptions
 into unchecked ones.  It's also called a thunk when used to delay evaluation.
 */
@FunctionalInterface
public interface Function0 extends Supplier, Callable {
    /** Implement this one method and you don't have to worry about checked exceptions. */
    U applyEx() throws Exception;

    /**
     The class that takes a consumer as an argument uses this convenience method so that it
     doesn't have to worry about checked exceptions either.
     */
    default U apply() {
        try {
            return applyEx();
        } catch (RuntimeException re) {
            throw re;
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    /** {@inheritDoc} */
    @Override default U get() { return apply(); }

    /** {@inheritDoc} */
    @Override default U call() throws Exception { return applyEx(); }

    // ========================================== Static ==========================================
    // Enums are serializable.  Anonymous classes and lambdas are not.
    enum Const implements Function0