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// Copyright 2022 Google LLC
//
// 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
//
//      https://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 dev.cel.runtime;

import java.util.Optional;

/**
 * Resolver for attribute lookups at runtime.
 *
 * Attributes identify resolvable parts of state available in the CEL expression.
 */
public interface CelAttributeResolver {
  /**
   * Attempts to resolve an attribute exactly.
   *
   * 
May return an UnknownSet if the attribute is unknown, a value if it has been resolved, or
   * Optional.empty() if the attribute isn't declared as an unknown.
   */
  Optional