Comparison of custom log4net Layout class I wrote in C# versus its F# equivalent.

GuidLayout.cs

public class GuidLayout : RawPropertyLayout
{
    public override object Format(LoggingEvent loggingEvent)
    {
        var baseFormat = base.Format(loggingEvent);
        
        if (baseFormat is Guid)
            return baseFormat;
        
        var guidString = baseFormat as string;
        if (guidString != null)
        {
            Guid guid;
            if (Guid.TryParse(guidString, out guid))
                return guid;
        }

        return null;
    }
}

GuidLayout.fs

type GuidLayout() =
    inherit RawPropertyLayout()

    override this.Format(loggingEvent) =
        match base.Format(loggingEvent) with
        | :? Guid as guid -> box guid
        | :? string as guidString -> 
            match Guid.TryParse(guidString) with
            | true, guid -> box guid
            | _ -> null
        | _ -> null