Re: Assertions in the Next Ada Standard

[Ed Falis <efalis@mediaone.net>]

FGD wrote:


>  From my perspective, invariants have many merits. The most important is 
> that it provides a uniform way of implementing all the type improvements 
> I ever thought of in a uniform way. I'm still not sure about 
> pre-/post-conditions. Right now, it seems to me that the associated 
> complexities outnumber the benefits and I'm still curious about 
> practical applications...

In the Eiffel model, the purpose of pre and post conditions is to 
establish the contract between caller and callee.  The practical benefit 
is that if a precondition is violated, then client code is where you 
look to find the problem;  if the postcondition is violated the service 
code is where you start.  An additional advantage of this approach is 
the elimination of code in services that would check explicitly for 
violations of the preconditions during deployment (the usual model is to 
enable pre and post condition checking during development, and to 
disable it during deployment).

- Ed