// Copyright 2014 The Bazel Authors. 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.syntax;

import com.google.common.collect.ImmutableCollection;
import javax.annotation.Nullable;

/** An interface for Skylark objects (such as structs) that have fields. */
public interface ClassObject {

  /**
   * Returns the value of the field with the given name, or null if the field does not exist.
   *
   * @throws EvalException if a user-visible error occurs (other than non-existent field).
   */
  @Nullable
  Object getValue(String name) throws EvalException;

  /**
   * Returns the names of the fields of this struct, in some canonical order.
   *
   * @throws EvalException if a user-visible error occurs
   */
  ImmutableCollection<String> getFieldNames() throws EvalException;

  /**
   * Returns the error message to print for an attempt to access an undefined field.
   *
   * <p>May return null to use a default error message.
   */
  @Nullable
  String getErrorMessageForUnknownField(String field);
}