src/main/java/com/google/devtools/build/lib/packages/PredicatesWithMessage.java

// Copyright 2014 Google Inc. All rights reserved.
//
// 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 com.google.devtools.build.lib.packages;

/**
 * A helper class for PredicateWithMessage with default predicates.
 */
public abstract class PredicatesWithMessage implements PredicateWithMessage<Object> {

  private static final PredicateWithMessage<?> ALWAYS_TRUE = new PredicateWithMessage<Object>() {
    @Override
    public boolean apply(Object input) {
      return true;
    }

    @Override
    public String getErrorReason(Object param) {
      throw new UnsupportedOperationException();
    }
  };

  @SuppressWarnings("unchecked")
  public static <T> PredicateWithMessage<T> alwaysTrue() {
    return (PredicateWithMessage<T>) ALWAYS_TRUE;
  }

}