Function0.java

/**
 * Licensed to The Apereo Foundation under one or more contributor license
 * agreements. See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership.
 *
 *
 * The Apereo Foundation licenses this file to you under the Educational
 * Community 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://opensource.org/licenses/ecl2.txt
 *
 * 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.opencastproject.util.data;

import static org.opencastproject.util.data.functions.Misc.chuck;

import org.opencastproject.util.data.functions.Functions;

/**
 * Function of arity 0, i.e. a constant function.
 *
 * @see X
 */
public abstract class Function0<A> {
  /** Apply function yielding a constant value. Don't be tempted to become impure! */
  public abstract A apply();

  /** Apply this function, then pass the result to <code>f</code>. */
  public <B> Function0<B> then(final Function<A, B> f) {
    return Functions.then(Function0.this, f);
  }

  /** Apply this function and ignore its result, then apply <code>f</code>. */
  public <B> Function0<B> then(final Function0<B> f) {
    return Functions.then(Function0.this, f);
  }

  /** Turn this function into an effect by discarding its result. */
  public Effect0 toEffect() {
    return Functions.toEffect(this);
  }

  /** Version of {@link Function0} that allows for throwing a checked exception. */
  public abstract static class X<A> extends Function0<A> {
    @Override
    public final A apply() {
      try {
        return xapply();
      } catch (Exception e) {
        return chuck(e);
      }
    }

    /**
     * Apply function to <code>a</code>. Any thrown exception gets "chucked" so that you may
     * catch them as is. See {@link Functions#chuck(Throwable)} for details.
     */
    public abstract A xapply() throws Exception;
  }
}