dynamic classes and duck typing

Walter Bright newshound1 at digitalmars.com
Wed Dec 2 03:11:20 PST 2009


retard wrote:
> Tue, 01 Dec 2009 14:24:01 -0800, Walter Bright wrote:
>> Unit tests have their limitations as well. Unit tests cannot prove a
>> function is pure, for example.
> 
> Sure, unit tests can't prove that.
> 
>> Both unit tests and static verification are needed.
> 
> But it doesn't lead to this conclusion. Static verification is sometimes 
> very expensive

Not if it's built in to the compiler. I aim to bring the cost of it down 
to zero.

> and real world business applications don't need those 
> guarantees that often.

Having your accounting software write checks in the wrong amount can be 
very very bad. And frankly, if you can afford your software unwittingly 
emitting garbage data, you don't need that software for your business apps.

> It's ok if a web site or game crashes every now 
> and then.

If Amazon's web site goes down, they likely lose millions of dollars a 
minute. Heck, I once lost a lot of business because the web site link to 
the credit card system went down. Few businesses can afford to have 
their ecommerce web sites down.

> If I need serious static verification, I would use tools like 
> Coq, not D..

There's a lot of useful stuff in between a total formal proof of 
correctness and nothing at all. D can offer proof of various 
characteristics that are valuable for eliminating bugs.



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