As an outsider to the Ruby-World but someone who has been burnt enough times by instances unexpectedly mutating themselves, I wonder: is it still a best practic

As an outsider to the Ruby-World but someone who has been burnt enough times by instances unexpectedly mutating themselves, I wonder: is it still a best practice in Ruby to mutate instances when computing values? Does Ruby somehow avoid the problems that you would encounter when doing this in JS/Java/C#?