From: John Carter <john.carter@...>
Date: 2005-09-23T09:18:05+09:00
Subject: Switching code in or out.

I tend to do a mix of Test Driven Development and Design By Contract.

I also tend to write code that chugs away for hours on a fast machine even 
when tightly optimized and all preconditions and invariants commented out.

Can anyone think of a convenient way of taking a class like....


class MyHairyClass
   def invariant
     raise "Invariant Failure: Bah" unless
        deep_expensive_check_on_the_invariants_of_the_class
   end

   def my_public_method( foo)
     invariant
     raise "Precondition failure: Blah" unless
       some_expression_involving_foo

     # DO STUFF

     raise "Postcondtion failure: Bloo" unless
       some_expression
     invariant
   end

end

and being able to selectively switch on and off the precondition and 
postcondition and pre and post invariant checks.

ie. I want all checks on maximum when I run the unit tests, I want them 
all switched off (compiled out) when I'm running the two hour long deep 
thought, and I want them selectively switched on when it crashes half way 
through the big run. eg. All the precond checks on.

The simplist would be...

if $debug
   def invariant
     # Do check
   end
else
   def invariant
   end
end

but that still does two method calls in some of my inner loops and doesn't 
handle the {pre,post}conditions nicely.

John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

Carter's Clarification of Murphy's Law.

"Things only ever go right so that they may go more spectacularly wrong later."

From this principle, all of life and physics may be deduced.