Assert

[Sean Kelly]

David B. Held wrote:
> BCS wrote:
>> Reply to David,
>>
>>> I think assert() will get fixed when we get AST macros.  It won't get
>>> fixed by Walter, of course, but rather, by us.  Everyone will invent
>>> their favorite assert(), and the builtin will only get called by
>>> Phobos.
>>> And then, 10 years down the road, Walter will be writing "The Design
>>> and Evolution of D", where he will have to explain why assert(o)
>>> doesn't
>>> do the obvious thing, even though everyone else's does. ;>
>>
>> what is there to fix? (that is not a rhetorical question)
> 
> Well, for one, the fact that "assert(obj)" doesn't do what 99% of noobs 
> (including me!) expect it to do.  Two, you can't write a custom assert() 
> that has non-standard messaging.  For instance, there is an extremely 
> common idiom in all languages (that support exceptions) that basically 
> looks like this:
> 
> if (!everything_ok)
> {
>     throw SomeException("Helpful message");
> }
> 
> Andrei happens to call this micro-pattern "enforce()", which I think is 
> a perfectly reasonable name for it.  What we would like to do is 
> something like so:
> 
> #define enforce(cond, message) \
>     if (!cond) throw SomeException(#cond + ": " + message);
> 
> Bar* ptr = foo();
> enforce(ptr != null, "foo() failed");
> 
> Obviously there's a thousand ways to riff on that basic idea, but try 
> writing this function in D.  As you can see, it's essentially a form of 
> assert().

Seems like the main problem is that assert is compiled out in release 
builds, correct?  Throwing a custom message and such already works.


Sean