That's definitely the right behavior for Ruby—it catches a contract violation and fails at runtime, which is idiomatic. What's nice about Rust's approach is that it catches the possibility of that contract violation at compile time, and forces you to decide what to do about it before the code ever runs. The right thing to do in Ruby would be to catch that exception and handle it in some fashion, but there is no indication at the time you're writing the code that the possibility exists, so you're unlikely to handle it unless you have a strong awareness of the issue with floats and NaN. Rust encodes that awareness into the language itself, which actually limits the expertise you need to write good code.
Merely chose that example to point out the absurdity of challenging Ruby on the grounds of flexibility (of all things).
Obviously, in a real program you'd rather write a custom sort-comparator, use a wrapper-class, or monkey-patch only the specific NaN instances that you want to change the behaviour of.
No, it's beautiful. Being a Python programmer it took me a long time to appreciate the power to do things like this. Learning Elisp, Smalltalk, Io and JavaScript (well) certainly helped.
Also, of course you can scope such a change however you want, for example to a single block (and with threadlocals it's going to be mostly safe).
He was just demonstrating that it is possible. You can in fact alias the method, do the sorting, and then restore the previous functionality of throwing errors. Plus, someone already mentioned that you can also use refinements.
Right, and the Rust equivalent would be to define a newtype that wraps your floating point type and defines the ordering semantics you want; in Ruby, you have changed the behavior for everything that uses Floats (including other libraries that may depend on this behavior), while in Rust you can use your newtype, other libraries can use standard floating point behavior, and you won't have any confusion about who wants which semantics.
and the Rust equivalent would be to define a newtype
Which you can do in Ruby as well, as I pointed out just two comments below the one you're replying to.
The real advantage of Rust here was imho best explained by sanderjd; Rust can perform this check at compile time whereas in Ruby it's a runtime exception.
