src/ProtocolBuffers/Descriptors/DescriptorUtil.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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// modification, are permitted provided that the following conditions are
// met:
//
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// in the documentation and/or other materials provided with the
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using System.Collections.Generic;
using Google.ProtocolBuffers.Collections;

namespace Google.ProtocolBuffers.Descriptors
{
    /// <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 Lists<TOutput>.AsReadOnly(array);
        }
    }
}