The entire Ruby ethos and surrounding APIs are basically all a result of a particular set of personal preferences. One of the core values of Ruby is programmer happiness. That’s obviously qualitative and varies from person to person. That said, this kind of pattern is extremely _Ruby_ and if you like it, you like it. I love writing Ruby code because of this kind of attention to making code almost like prose. However, I’ve also worked on a lot of terrible Ruby projects that were a mess of metaprogramming and clever dynamic language abuse, so it’s hard to mount a rigorous defense.

There are languages which can automatically transform between a.foo(b) and foo(a, b) - for example the D language. Does this make 2.weeks.from_now more palatable? And if it does, then why worry about whether the code “goes on the class” or not? During execution it doesn’t really matter where the code lives, and during development open classes are doing basically the same thing as defining functions overloaded on the first argument.

That looks like you're having to make a Weeks class just so you can do the same thing, instead of adding it to Integer and having it available on any int.