package jetbrains.jetpad.base;

public abstract class BaseRegistration implements Registration {
  public static Registration empty() {
    return new BaseRegistration() {
      @Override
      protected void doRemove() {
      }
    };
  }

  private boolean myRemoved;

  protected abstract void doRemove();

  @Override
  public final void remove() {
    if (myRemoved) {
      throw new IllegalStateException();
    }
    doRemove();
    myRemoved = true;
  }
}

/*
 * Copyright 2012-2015 JetBrains s.r.o
 *
 * 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 jetbrains.jetpad.base;

public abstract class BaseRegistration implements Registration {
  public static Registration empty() {
    return new BaseRegistration() {
      @Override
      protected void doRemove() {
      }
    };
  }

  private boolean myRemoved;

  protected abstract void doRemove();

  @Override
  public final void remove() {
    if (myRemoved) {
      throw new IllegalStateException();
    }
    doRemove();
    myRemoved = true;
  }
}

add liscence to BaseRegistration