From: Terry Poulin <bigboss64@...>
Date: 2007-09-08T06:01:16+09:00
Subject: Re: Is this a bug or a feature?

>>
>> I think what Martin wants is a bottom-tested loop, but I don't believe
>> Ruby has that. until is a top-tested loop just like while. The only way I
>> know to get bottom-tested behavior is this.
>>
>> loop do
>> # some code goes here
>> break if condition
>> end
>
> You can do:
>
>   begin
>     # do stuff
>   end until condition
>
>
> David
>

irb(main):001:0> i = 0
=> 0
irb(main):002:0> until (i+=1) >5 do
irb(main):003:1*   p i
irb(main):004:1> end
1
2
3
4
5
=> nil
irb(main):005:0>


Because i is incremented at each passage of the loop, _before_ it starts the
loop if i is 1 when i+=1 is evaluated it becomes 2 when you try to print it.

It's nether a bug nore a feature IMHO. If you *do* want to have a bottom
tested loop much as David just said;

irb(main):001:0> i = 1
=> 0
irb(main):002:0> begin
irb(main):003:1*   puts i
irb(main):004:1> end until (i+=1)>5
1
2
3
4
5
=> nil
irb(main):005:0>

Works fine with i equal to 1 before starting the loop -> because it prints i
before it is changed when i+=1 is evaluated before the second pass through the
block is made.



If you do find a need to use a test at the bottom instead of the top, you
should ether 0.) Keep the body of the loop short or 1.) Make it explicit to
the reader that a loop is starting.


Generally I avoid code like that because If six months later you don't know
(or that a loop is starting until you see the until expression, it's more
trouble then following a more conventional style.

If you ask me, if the body of a loop grows to long that you don't remember why
the loop was executing when you hit the end of it, thats a problem in of it
self any way ;-)


TerryP.




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