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Mark Leighton Fisher (4252)

Mark Leighton Fisher
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http://mark-fisher.home.mindspring.com/

I am a Systems Engineer at Regenstrief Institute [regenstrief.org]. I also own Fisher's Creek Consulting [comcast.net].
Friday June 16, 2006
12:10 PM

Design by Contract: Not with lvalue subs

[ #29928 ]

I'd thought that I would write about using Design by Contract preconditions and postconditions with Perl and VB. I had not used Perl lvalue subs before, but I thought it would be easy to use an lvalue sub to perform data validation as preconditions and postconditions. After much experimentation, then some Googling, I finally found a post about lvalue subs on Perl Monks explaining that you can't actually do anything with the value while you are in the lvalue sub:

  1. You can't examine the proposed new value before the assignment; and
  2. You can't check the value after assigning it.

Thus endeth the lesson for the day.

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