When I come across an `unless`, I can't use them; I have to come back out into "conscious reading" mode, or something like that. Makes me crazy.
do_something unless already_done?Anything else (at least for me) is more difficult to read, it's probably due to being exposed to all thos other languages that do not have that syntactic construct. Using C syntax conditionals feels more natural to me, but again this is all opinionated.
Problem with so much syntactic sugar is you need to retain/recall the semantics of the vocabulary. As a polyglot programmer who doesn't write much code anymore, it slows me down.
That said, I feel it's really down to double+ negation being hard to handle. `if` with a single negation is fine; `unless` is automatically a negation, so you're just off to a bad start on that front. I feel like the only viable use is in a case like Rust's `let … else { diverge }` where anything that fails the condition is guaranteed to diverge (typically, return) and I can just ignore it when reading the overall codeflow. But Ruby mixes that up and does `diverge unless …` which puts the diverging part "up front" and "in the way" for such readings.
Weirdly, Ruby was one of the first languages I learned early in my career, and at the time I had no problem with `unless`. But after years of experience with other languages, I similarly feel that `if` statements now trigger the fast pattern matching circuits in my brain, while `unless` makes me do a double-take and basically translate it into `if not`
At first I thought I was just becoming dumber with age, but I like your explanation better :P