It's not really quite accurate to say that you no longer define your own new. It's merely the case that you get a default new for free. However, that default constructor only handles named parameters. If you want a constructor that uses positional parameters, you have to define your own, and there's no reason you can't call it call it new if you like, presuming it's something that multimethod dispatch can sort out from the default Object.new().

By the way, I disagree slightly with chromatic on this point. I think new Foo without colon is just fine, since we've gone to some pains to make sure that 1) it works as MMD and that 2) neither the method name nor the class name are taken as barewords. You could just as easily write new(Foo) and it will still work via MMD. But there's nothing wrong with the colon, and different people value different kinds of consistency.