test-serilog-destructure.cs

using Serilog;
using Serilog.Core;
using Serilog.Events;

Log.Logger = new LoggerConfiguration()
        .WriteTo.Console(formatProvider:new GuidFormatter())
            .Destructure.With<GuidDestructuringPolicy>()
            .Destructure.ByTransforming<CustomClass>(Helper.ToString)
            .Destructure.ByTransforming<CustomStruct>(Helper.ToString)
        .CreateLogger();

Log.Information("Hello, {@Guid}!", Guid.NewGuid());
Log.Information("Hello, {@CustomClass}!", new CustomClass { I = 1 });
Log.Information("Hello, {@CustomStruct}!", new CustomStruct());

static class Helper
{
    public static object ToString(Guid guid)
    {
        return guid.ToString().Substring(0,5);
    }

    public static object ToString(CustomClass zxc)
    {
        return $"zxc: {zxc.I}";
    }

    public static object ToString(CustomStruct asd)
    {
        return $"asd: {asd.J}";
    }
}

readonly struct CustomStruct
{
    public int J { get; }
}

class CustomClass
{
    public int I { get; set; }
}


// doesn't work because Guid considered as scalar type
public class GuidDestructuringPolicy : IDestructuringPolicy
{
    public bool TryDestructure(object value, ILogEventPropertyValueFactory propertyValueFactory, out LogEventPropertyValue result)
    {
        if (value is Guid guid)
        {
            result = propertyValueFactory.CreatePropertyValue(Helper.ToString(guid));
            return true;
        }

        result = default;
        return false;
    }
}

// Dummy custom formatter to illustrate idea
class GuidFormatter : IFormatProvider, ICustomFormatter
{
    public GuidFormatter()
    {
    }

    public string Format(string? format, object? arg, IFormatProvider? formatProvider)
    {
        if (arg is Guid guid)
        {
            return Helper.ToString(guid).ToString();
        }

        return arg.ToString();
    }

    public object GetFormat(Type formatType)
    {
        if (formatType == typeof(ICustomFormatter))
            return this;
        else
            return null;
    }
}