From: James Edward Gray II <james@...>
Date: 2005-12-14T10:36:50+09:00
Subject: Re: Idiom wanted: do-while

On Dec 13, 2005, at 7:20 PM, Steve Litt wrote:

> On Tuesday 13 December 2005 11:09 am, Jacob Fugal wrote:
>> On 12/12/05, Steve Litt <slitt@earthlink.net> wrote:
>>> On Monday 12 December 2005 05:42 pm, James Edward Gray II wrote:
>>>> loop do
>>>>    # ... some action ...
>>>>    break unless ...
>>>> end
>>>
>>> I do this quite a bit, but it's not structured programming and is a
>>> little like a goto.
>>
>> I see no similarity. 'goto' is unstructured because the target point
>> is completely arbitrary; place a label in your code then jump  
>> right to
>> it. 'break' is completely structured; it's part of the structure of
>> the enclosing loop and its target is defined by that structure.
>
> Ahh -- I found a reference. See
> http://en.wikipedia.org/wiki/Structured_programming, and note  
> Dijkstra's
> structured programming definition -- every block of code has one  
> entry point
> and one exit point.

The loop do ... end construct is infinite.  You must add a break to  
end it.  With one break, it has exactly one entry and exit point.

>>> Break can improve readability on small loops, but on large loops
>>> maintained by multiple people it can become a nightmare.
>>
>> I agree with James; if the loop is long enough or complex enough for
>> these to be a problem, the body of the loop probably needs some
>> serious refactoring.
>
> It absolutely does. Trouble is, in many shops loops start out 8  
> lines of code,
> and over many, many years, maintenance programmers, many not  
> experienced,
> most not being privy to original design considerations, add  
> features demanded
> by management on ultra-tight schedules. A few years later it's 100  
> lines of
> code and the break statement is in the middle of it.

You may be describing where you work, but you are certainly not  
describing where I do.  ;)

I've got two words for you:  Unit tests.  They were invented to  
address every single issue you just listed (plus some!) and I assure  
you, they work.  You really, really should give them a try.  It will  
be the best gift you ever give yourself, I promise.

James Edward Gray II