How to deserialize an immutable data structure?

Question

How would I deserialize YAML to a immutable data structure?

e.g. I have this YAML:

Value: SomeString
Number: 99

And this data structure:

public class MyData
{
    public MyData(string value, int number)
    {
        Value = value;
        Number = number;
    }

    public string Value { get; }
    public int Number { get; }
}

For this I'd to use the constructor. So somehow I'd need to first retrieve a Dictionary<string, object> parsed from the YAML respecting my class (so 99 would be int, not string), then scan my type for an appropriate constructor,

Answer 1

Although the question doesn't mention it, I'm assuming you are using YamlDotNet (or SharpYaml which is a fork of YamlDotNet)

YamlDotNet doesnt support deserializing into classes that do not have a default constructor - but one option to achieve what you want is to deserialize into an intermediate Builder type that is mutable which can produce the final type. e.g.

public class MyDataBuilder
{
    public string Value { get; set; }
    public int Number { get; set; }
    public MyData Build() => new MyData(Value, Number);
}

And then use something like:

deserializer.Deserialize<MyDataBuilder>(yaml).Build();

You would end up having to create a parallel set of builders for your whole model however, e.g. if MyData had a third parameter of type MyOtherData (I've changed the example to use records instead of classes to make it concise):

public record MyOtherData(string OtherValue);
public record MyData(string Value, int Number, MyOtherData otherData);

In which case we would need another Builder:

public class MyOtherDataBuilder 
{
    public string OtherValue { get; set; }
}

And MyDataBuilder would look like:

public class MyDataBuilder
{
    public string Value { get; set; }
    public int Number { get; set; }
    public MyOtherDataBuilder MyOtherData { get; set; }
    public MyData Build() => new MyData(Value, Number, MyOtherData.Build());
}