// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// http://github.com/jskeet/dotnet-protobufs/
// Original C++/Java/Python code:
// http://code.google.com/p/protobuf/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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using System.Collections.Generic;
using System.Collections.ObjectModel;

namespace Google.ProtocolBuffers.Collections {

  /// <summary>
  /// Utility non-generic class for calling into Lists{T} using type inference.
  /// </summary>
  public static class Lists {

    /// <summary>
    /// Returns a read-only view of the specified list.
    /// </summary>
    public static IList<T> AsReadOnly<T>(IList<T> list) {
      return Lists<T>.AsReadOnly(list);
    }
  }

  /// <summary>
  /// Utility class for dealing with lists.
  /// </summary>
  public static class Lists<T> {

    static readonly ReadOnlyCollection<T> empty = new ReadOnlyCollection<T>(new T[0]);

    /// <summary>
    /// Returns an immutable empty list.
    /// </summary>
    public static ReadOnlyCollection<T> Empty {
      get { return empty; }
    }

    /// <summary>
    /// Returns either the original reference if it's already read-only,
    /// or a new ReadOnlyCollection wrapping the original list.
    /// </summary>
    public static IList<T> AsReadOnly(IList<T> list) {
      return list.IsReadOnly ? list : new ReadOnlyCollection<T>(list);
    }
  }
}