有没有办法在protobuf-net代理类中定义替代转换函数(从/到接口)

Question

使用protobuf-net v2 build 668,我正在尝试序列化/反序列化一个类,该类包含一个定义为接口的成员,同时进行即时转换.通常,代理方法可以正常工作,但由于C#不允许用户定义的接口转换,我无法定义转换.

谢谢,

namespace ProtoBufNetTest
{
    using System.Diagnostics;
    using System.IO;

    using ProtoBuf;
    using ProtoBuf.Meta;

    class Program
    {
        static void Main()
        {
            RuntimeTypeModel.Default.Add(typeof(IDummy), false)
                .SetSurrogate(typeof(DummySurrogate));

            var container = new Container { Data = new Dummy { Positive = 3 } };

            using (var file = File.Create("test.bin"))
            {
                Serializer.Serialize(file, container);
            }

            using (var file = File.OpenRead("test.bin"))
            {
                container = Serializer.Deserialize<Container>(file);
                Debug.Assert(container.Data.Positive == 3);
            }
       }
    }

    // Outside of the project, cannot be changed
    public interface IDummy
    {
        int Positive { get; set; }
    }

    [ProtoContract]
    public class Container
    {
        [ProtoMember(1)]
        public IDummy Data { get; set; }
    }

    public class Dummy : IDummy
    {
        public int Positive { get; set; }
    }

    [ProtoContract]
    class DummySurrogate
    {
        [ProtoMember(1)]
        public int Negative { get; set; }

        // Does not compile : user-defined conversions to or from an interface are not allowed
        public static explicit operator IDummy(DummySurrogate value)
        {
            return value == null ? null : new Dummy { Positive = -value.Negative };
        }

        // Does not compile : user-defined conversions to or from an interface are not allowed
        public static explicit operator DummySurrogate(IDummy value)
        {
            return value == null ? null : new DummySurrogate { Negative = -value.Positive };
        }

        // Fake attribute, does not exist but could work if it did
        [ProtoConvertFrom]
        public static IDummy From(DummySurrogate value)
        {
            return value == null ? null : new Dummy { Positive = -value.Negative };
        }

        // Fake attribute, does not exist but could work if it did
        [ProtoConvertTo]
        public static DummySurrogate To(IDummy value)
        {
            return value == null ? null : new DummySurrogate { Negative = -value.Positive };
        }
    }
}

Answer 1

在当前版本中：不，没有。

然而，在下一个版本中，这工作得很好：

[ProtoContract]
class DummySurrogate
{
    [ProtoMember(1)]
    public int Negative { get; set; }

    [ProtoConverter]
    public static IDummy From(DummySurrogate value)
    {
        return value == null ? null : new Dummy { Positive = -value.Negative };
    }

    [ProtoConverter]
    public static DummySurrogate To(IDummy value)
    {
        return value == null ? null : new DummySurrogate
           { Negative = -value.Positive };
    }
}

基本上，static标记的方法[ProtoConverter]优先于定义的implicitorexplicit转换运算符，其进一步的优点是[ProtoConverter]方法不受与运算符相同的语法规则的约束。没有必要定义单独的*To/*From属性，因为签名的意图很明确。

附带说明： 上的属性Dummy是不必要的，并且从不使用。