Contracts or Exceptions?

[Steven Schveighoffer]

On Tue, 29 Mar 2011 14:40:02 -0400, Mike Linford  
<mike.linford.reg at gmail.com> wrote:

> Hello,
>
> So I'm writing a function for a library. It takes a struct as an
> argument. The struct's fields can't just be any old values, though. The
> function won't work if some of the fields are weird. It could return an
> erroneous value, or even crash.
>
> The thing is, though, that I can't tell whether the best approach is to
> use an in-contract or throw an exception if it doesn't pass my test. What
> would you guys recommend?

This has been discussed very recently on the main newsgroup  
(digitalmars.D).  It is not an easy question to answer.

There are two ways to answer it easily:  1. if the input to the function  
will always be deterministic, meaning there is no chance some  
environmental cause can affect the input, or the validity of the input,  
then use contracts, this should catch any code errors during testing.  2.  
if the input to the function will always be generated external to the  
program (i.e. from a file), then you should use exceptions.

If it could be either, there are different schools of thought on this.  If  
the function isn't performance critical, throwing an exception is likely a  
good choice.  However, if it is performance critical, I'd recommend using  
contracts.  Then if you have a situation when your input is externally  
generated, you need to check it outside the function with an exception  
thrown on error.

-Steve