Assert and the optional Message

[Timon Gehr]

On 03/09/2012 07:37 PM, H. S. Teoh wrote:
> On Fri, Mar 09, 2012 at 07:23:20PM +0100, Timon Gehr wrote:
>> On 03/09/2012 05:56 PM, Jonathan M Davis wrote:
> [...]
>>> It was never intended that AssertError or any other Error be
>>> particularly catchable, but it's also true that D is a systems
>>> programming language, so it'll let you do stuff which is unsafe, so
>>> if you know what you're doing, then there are circumstances where you
>>> can get away with (unit testing is one example of where catching
>>> AssertErrors might make sense). But you have to know what you're
>>> doing, since it's _not_ safe.
>>>
>>> - Jonathan M Davis
>>
>> AssertErrors must be recoverable because of the way contracts work.
>
> Are you referring to contract AssertErrors in unittests, or in general?
>
> In general, I think contracts *should* terminate the program with
> extreme prejudice when they fail. It represents assumptions about
> internal consistency being broken, which makes it unsafe to do
> otherwise.
>
> But in unittests where these assumptions are deliberately broken (to
> ensure the contract does what you think it does), it makes sense to be
> able to "recover" from AssertErrors.
>
>
> T
>

'in' contracts must catch assertion failures because it is enough if one 
of them passes.


class Foo{
     void foo(int x)in{assert(x==0);}body{}
}
class Bar: Foo{
     void foo(int x)in{assert(x==1);}body{}
}

void main(){
     Bar bar = new Bar;
     bar.foo(0); // ok
     bar.foo(1); // ok
}