cs
    public class MyMappingDefinition : IMapDefinition
    {
        private readonly IMyCoolService _mycoolService;

        public MyMappingDefinition(IMyCoolService mycoolService)
        {
            _mycoolService = mycoolService;
        }

        public void DefineMaps(IUmbracoMapper mapper)
        {
            mapper.Define<ISomething, SomethingElse>((_, _) => new SomethingElse(), Map);
        }

        private void Map(ISomething source, SomethingElse target, MapperContext)
        {
            _mycoolService.DoSomethingReallyCool();

            // do mapping
        }
    }