Ruby’s Most Underused Keyword

My personal up until recently underused keyword was (surprise!) "rescue".

I'm not sure how this has been escaping me since 07, but I had no idea you can apply it at the end of an expression, i.e. when you're facing nasty functions that insist on trhowing exceptions, instead of

begin

  value = function_that_throws

rescue

  value = "default"

end

you can just write:

value = function_that_throws rescue "default"

redo, in the Fibonacci example, is still iterative - it's presented as a third way, when it's just a cruftier way of being iterative. If you remove the cruft of the lambda and the redo, you end up with:

  def fib(i)
    n, result = 1, 0
    while i != -1
      i, n, result = i - 1, n + result, n
    end
    result
  end

Cleaner, faster (by 10% on Ruby 1.8) and shorter, but certainly iterative.

(Separate to this, the fib routines shown produce incorrect results - my example above maintains this, just for comparison with the original code. fib(10) is 55 not 89 - it's one off in its input.)

Using redo for tail recursion in Ruby is an interesting idea, similar to Clojure's recur keyword.