Truly @nogc Exceptions?

[Steven Schveighoffer]

On 9/20/18 11:33 AM, Adam D. Ruppe wrote:
> On Wednesday, 19 September 2018 at 21:16:00 UTC, Steven Schveighoffer 
> wrote:
>> As Andrei says -- Destroy!
> 
> Nah, I agree. Actually, I'm of the opinion that string error messages in 
> exceptions ought to be considered harmful: you shouldn't be doing 
> strings at all. All the useful information should be in the type - the 
> class name and the members with details.
> 
> Well, defining a new class can sometimes be a mild hassle... but for 
> really common ones, we really should just do it, and other ones can be 
> done as templated classes or templated factory functions that define a 
> new class right there and then.
> 
> http://arsdnet.net/dcode/exception.d
> 
> That's the proof-of-concept I wrote for this years ago, go to the bottom 
> of the file for the usage example. It uses a reflection mixin to make 
> writing the new classes easy, and I even wrote an enforce thing that can 
> add more info by creating a subclass that stores arguments to functions 
> so it can print it all (assuming they are sane to copy like strings or 
> value things lol)
> 
>      enforce!fopen("nofile.txt".ptr, "rb".ptr);
> 
> MyExceptionBase at exception.d(38): fopen call failed
>          filename = nofile.txt
>          mode = rb
> ----------------


Awesome! This is just what I was thinking of. In fact, I did something 
similar locally since I needed to know what the slice parameters that 
were failing were. I still had to trick the @nogc to get around the "new 
Exception" piece.

The printMembers thing is nice. I think for druntime/phobos, however, we 
should have a base that just calls a virtual function with the idea that 
the message is printed, and then a further-derived type could do the 
printMembers thing if that's what you want.

-Steve