ClassStuctBinder<T> replace fields of default value

[gODeaLoAple]

ClassStructBinder sets values from ISettingNode recursively to provided default value. So it can change even some static readonly field of another class.
For example:

public class MessageFormat
{
    public static readonly MessageFormat Default  = new MessageFormat() { Format = "C" };
    public string Format { get; set; }
}

public class AppSettings 
{
    public MessageFormat DefaultFormat { get; set; } = MessageFormat.Default;
    public MessageFormat SpecificFormat { get; set; } = MessageFormat.Default;
}

So, if we provide object source to ConfigurationProvider:

configurationProvider.SetupSourceFor<AppSettings>(new ObjectSource(new AppSettings()
{
    DefaultFormat = new MessageFormat() { Format = "A" },
    SpecificFormat = new MessageFormat() {Format = "B" }
}));
var settings = provider.Get<AppSettings>();

Console.WriteLine(settings.DefaultFormat.Format); // B
Console.WriteLine(settings.SpecificFormat.Format); // B
Console.WriteLine(MessageFormat.Default.Format); // B

Maybe ConfigurationProvider should create object copy instead of changing existing object or even throw any exception, or print warning about this issue

[kunga]

This code is wrong even without ConfigurationProvider:

auto settings1 = new MessageFormat();
settings1.SpecificFormat.Format = "B";

auto settings2 = new MessageFormat();
Console.WriteLine(settings.SpecificFormat.Format); // B

Or do you really expect that behaviour if you see that code?

[gODeaLoAple]

Maybe some users expect that ConfigurationProvider copy an object and call setters on it instead of changing the orgin. For example this case appeared recently: user had set a default value and could not understand why another object changed too. I think we should at least warn users about this non-obvious behavior in some way. Or just copy an object before set values