protobuf/src/ProtocolBuffers/Collections/Lists.cs

// 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/
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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);
    }
  }
}