assert(0) behavior

[Jonathan M Davis via Digitalmars-d]

On Wednesday, 5 August 2015 at 02:52:40 UTC, Jonathan M Davis 
wrote:
> On Tuesday, 4 August 2015 at 22:13:40 UTC, Steven Schveighoffer 
> wrote:
>> On 8/4/15 5:39 PM, Jonathan M Davis wrote:
>>
>>> I'm certainly not opposed to have a message be printed before 
>>> the HLT
>>> instruction with assert(0), but I don't at all agree that the 
>>> fact that
>>> the message is not seen in -release is a reason not to have a 
>>> message.
>>
>> For instance:
>>
>> https://github.com/D-Programming-Language/druntime/blob/master/src/core/time.d#L2283
>>
>> This makes it seem like a message will be printed in the case 
>> where ticksPerSecond was 0. but in reality it simply throws a 
>> segfault.
>>
>> Whether this happens or not in debug mode is pretty much 
>> irrelevant -- druntime is used in release mode by the vast 
>> majority of all developers, and this passes unit tests for us. 
>> It's the whole impetus for this thread, because someone 
>> actually did find a case where it gets there.
>>
>> So why have a message with the clock name that failed? Why not 
>> just assert(0)? The only purpose I see for such a message is 
>> to trick the reviewer into accepting it (not that this was the 
>> intention of course) as being sufficiently explanatory when an 
>> error occurs.
>>
>> We should always review such code with the view that when it 
>> *doesn't* print the message, is the error sufficient to a user 
>> such that they know where to look. I find it hard to believe 
>> it's *ever* sufficient, if you needed to have a message in the 
>> first place.
>>
>> We can look at it this way -- if you need to add a message to 
>> an assert(0) for it to make sense, you should find a different 
>> way to communicate that.
>
> It was never expected that a user to see any of those messages 
> anyway. The idea was that if they failed, there was something 
> seriously wrong, and the program needed to be killed. If the 
> message prints when it fails, great. It's more explanatory that 
> way, but it's a bonus (and one that you do get if druntime is 
> build in debug mode). The purpose was to kill the program, 
> because it was in an invalid state.

Maybe in this case, it would have made more sense to simply throw 
an Error rather than use assert(0), since it inadvertently ended 
up depending on the system's environment, even though it was 
supposed to be guaranteed to work (differences in kernel versions 
was not taken into account). And I assume that if we threw an 
Error, then we'd get a message.

- Jonathan M Davis