Not sure what you mean with applying only to instances, in which case couldn't you use an extension method? If you own the code making a function an extension m

Not sure what you mean with applying only to instances, in which case couldn't you use an extension method? If you own the code making a function an extension method seems not a big deal. If you want to invoke a static function you don't own the code for then you could have a generic wrapper extension method which admittedly would probably look rather clumsy and nullify the desired gain in readability.