Comment by tomphoolery

I think the argument here is to embrace the immutability of arrays in Ruby. The reason why this is called `reject!` rather than `reject` is because the designers of Ruby wanted you to favor returning new objects rather than mutating objects in place. Sure, you might need to do it from time-to-time and I'm really happy we have methods that enable such behavior, but this brings to mind the old adage "just because you can, doesn't mean you should". The author might have been trying to say in that quote that app developers should find other ways of solving whatever problem they have without resorting to mutating objects in place. I don't think we should go as far as to not include such methods in Ruby if everyone finds them useful from time-to-time, but I also think we should be staying away from mutating objects in place, rather than returning new versions of said objects and using that.