protobuf/csharp/src/ProtocolBuffers/FieldAccess/FieldAccessorTable.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/
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//
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// in the documentation and/or other materials provided with the
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#endregion

using System;
using System.Collections.ObjectModel;
using Google.Protobuf.Descriptors;

namespace Google.Protobuf.FieldAccess
{
    /// <summary>
    /// Provides access to fields in generated messages via reflection.
    /// </summary>
    public sealed class FieldAccessorTable
    {
        private readonly ReadOnlyCollection<IFieldAccessor> accessors;
        private readonly MessageDescriptor descriptor;

        /// <summary>
        /// Constructs a FieldAccessorTable for a particular message class.
        /// Only one FieldAccessorTable should be constructed per class.
        /// </summary>
        /// <param name="type">The CLR type for the message.</param>
        /// <param name="descriptor">The type's descriptor</param>
        /// <param name="propertyNames">The Pascal-case names of all the field-based properties in the message.</param>
        public FieldAccessorTable(Type type, MessageDescriptor descriptor, string[] propertyNames)
        {
            this.descriptor = descriptor;
            var accessorsArray = new IFieldAccessor[descriptor.Fields.Count];
            for (int i = 0; i < accessorsArray.Length; i++)
            {
                var field = descriptor.Fields[i];
                var name = propertyNames[i];
                accessorsArray[i] =
                    field.IsMap ? new MapFieldAccessor(type, name, field)
                    : field.IsRepeated ? new RepeatedFieldAccessor(type, name, field)
                    : (IFieldAccessor) new SingleFieldAccessor(type, name, field);
            }
            accessors = new ReadOnlyCollection<IFieldAccessor>(accessorsArray);
            // TODO(jonskeet): Oneof support
        }

        // TODO: Validate the name here... should possibly make this type a more "general reflection access" type,
        // bearing in mind the oneof parts to come as well.
        /// <summary>
        /// Returns all of the field accessors for the message type.
        /// </summary>
        public ReadOnlyCollection<IFieldAccessor> Accessors { get { return accessors; } }

        public IFieldAccessor this[int fieldNumber]
        {
            get
            {
                FieldDescriptor field = descriptor.FindFieldByNumber(fieldNumber);
                return accessors[field.Index];
            }
        }

        internal IFieldAccessor this[FieldDescriptor field]
        {
            get
            {
                if (field.ContainingType != descriptor)
                {
                    throw new ArgumentException("FieldDescriptor does not match message type.");
                }
                return accessors[field.Index];
            }
        }
    }
}