csharp/src/Google.Protobuf/Reflection/DescriptorUtil.cs

#region Copyright notice and license
// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// 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,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#endregion

using System.Collections.Generic;
using System.Collections.ObjectModel;

namespace Google.Protobuf.Reflection
{
    /// <summary>
    /// Internal class containing utility methods when working with descriptors.
    /// </summary>
    internal static class DescriptorUtil
    {
        /// <summary>
        /// Equivalent to Func[TInput, int, TOutput] but usable in .NET 2.0. Only used to convert
        /// arrays.
        /// </summary>
        internal delegate TOutput IndexedConverter<TInput, TOutput>(TInput element, int index);

        /// <summary>
        /// Converts the given array into a read-only list, applying the specified conversion to
        /// each input element.
        /// </summary>
        internal static IList<TOutput> ConvertAndMakeReadOnly<TInput, TOutput>(IList<TInput> input,
                                                                               IndexedConverter<TInput, TOutput>
                                                                                   converter)
        {
            TOutput[] array = new TOutput[input.Count];
            for (int i = 0; i < array.Length; i++)
            {
                array[i] = converter(input[i], i);
            }
            return new ReadOnlyCollection<TOutput>(array);
        }
    }
}