Serialize type to an arbitrary string

Question

I've declared a struct TaxpayerIdentificationNumber, that contains private long and represents 13 digits. I want to be able to serialize it into a mere string, that contains that private number (padded with zeros in front, but never mind it).

For example, we have DateTime, that serializes to "2020-01-01T00.00.01" and not to "{'ticks': 34546 }". I want that special treatment for my types too. And deserialization from a simple string as well.

I've explored ISerialized and its associated method and constructor, but didn't eventually understand, how to just define the method, which will form the final string I want.

Answer 1

It looks like you're doing JSON serialization; so, something like this, assuming you're using Newtonsoft.Json?

using Newtonsoft.Json;
using System;

var obj = new HazFoo { Value = new("whatever") };
var json = JsonConvert.SerializeObject(obj); // {"Value":"whatever"}
Console.WriteLine(json);
var clone = JsonConvert.DeserializeObject<HazFoo>(json);
Console.WriteLine(clone.Value.TaxpayerIdentificationNumber); // whatever

class HazFoo
{
    public Foo Value { get; set; }
}

[JsonConverter(typeof(FooConverter))]
readonly struct Foo : IEquatable<Foo>
{
    public string TaxpayerIdentificationNumber { get; }

    public Foo(string id) => TaxpayerIdentificationNumber = id;

    private sealed class FooConverter : JsonConverter<Foo>
    {
        public override Foo ReadJson(JsonReader reader, Type objectType, Foo existingValue, bool hasExistingValue, JsonSerializer serializer)
            => new Foo((string)reader.Value);

        public override void WriteJson(JsonWriter writer, Foo value, JsonSerializer serializer)
            => writer.WriteValue(value.TaxpayerIdentificationNumber);
    }

    // these have nothing to do with serialization, but are good practice
    // for value-types, to avoid unnecessary boxing
    public override bool Equals([NotNullWhen(true)] object obj)
        => obj is Foo other && Equals(other);
    public override int GetHashCode()
        => TaxpayerIdentificationNumber?.GetHashCode() ?? 0;
    public override string ToString()
        => TaxpayerIdentificationNumber;
    public bool Equals(Foo other)
        => TaxpayerIdentificationNumber == other.TaxpayerIdentificationNumber;
}