Ruby’s Most Underused Keyword

http://www.rubyrailways.com/rubys-most-underused-keyword/

by sant0sk1 • 17 years ago

50 12 17 years ago

jimbokun• 17 years ago

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

sunkencity• 17 years ago

but ruby doesn't support tail recursion effectively? or is this something new in 1.9. Stack level is not deep enough in 1.8 :P

judofyr2• 17 years ago

1.9 supports it, together with some other optimizations, but everything is turned off in 1.9.1. 1.9.2 will be sweet :-)

old-gregg2• 17 years ago

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"

sc• 17 years ago

Cool, sure, but blind rescues are as the crow flies to bugs: use them wisely, or use them _why-ly.

iamwil2• 17 years ago

that's along the lines of using or for nil returns.

value = function_that_nils || "default"

I've found it makes code more succinct.

old-gregg2• 17 years ago

Careful here: I've seen plenty of "Rubiomatic" bugs that look like this:

value = function_that_nils or "default"

... which results in nil assignment to value. Accidental confusion between || and 'or' is very common in Ruby world IMO, almost like famous == vs = in C.

petercooper2• 17 years ago

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.)

judofyr2• 17 years ago

You are absolutely right... if you're an interpreter...

From a user's point of view, the redo says "run this block again"; and since the block == the method it's just another way to run acc(). Of course, it's still faking, but I've never claimed anything else :-)

petercooper2• 17 years ago

Since we're having the discussion in two places, I'll be quicker here.. ;-)

"run this block again" signifies "loop" to me and "loop" signifies "iteration." If I see a block of code being looped, I don't think (as a coder, not as an interpreter) that it's recursive. Perhaps others would, though. If we got in a time machine back to the 80s, I kinda feel that "redo" would turn into "goto".. :)

(Hey, we should be doing this on RubyFlow as well - you could be earning some serious karma :))

DougBTX• 17 years ago

Simplistically, tail call optimisation is an automated way to convert recursion into iteration. You could do that by hand for any tail call recursive function, whether you do so is a function of style and the language you are using.

Ruby’s Most Underused Keyword

Related Stories