DIP33: A standard exception hierarchy

[Lars T. Kyllingstad]

On Wednesday, 3 April 2013 at 00:07:10 UTC, Jonathan M Davis 
wrote:
> [...]
> If we had IllegalArgumentException, it would likely be the base 
> class for some
> subset of exceptions which were always bad arguments, but it 
> certainly
> wouldn't make sense to use it by itself in most cases. It would 
> just provide a
> convenient way to catch that particular subset of exceptions if 
> you needed to.

I disagree.  Some things don't really deserve a more detailed 
error than just "illegal argument".  Examples include passing a 
negative number where a positive one was expected, an invalid 
combination of bit flags, an invalid file mode to a file-opening 
function, etc.


> In general though, I think that assert covers what 
> IllegalArgumentError is
> trying to do just fine, and where it doesn't, the argument 
> about needing more
> descriptive exceptions applies just as well (e.g. RangeError). 
> [...]

The problem with assert is that it gets disabled in release mode. 
  I think it is a bad idea to have this be the "standard" 
behaviour of parameter validation.


> [...]
>
> If you're treating Error exclusively as programming errors, 
> then it's really
> no different from AssertError. You're just creating categories 
> for specific
> types rather than using assert for them all.

Wouldn't you say that most of the Error types we have today do, 
in fact, signal programming errors?  Walter even argued that 
OutOfMemoryError is often a programming error.


> [...]
>
> So, unless you're arguing that assertions should be left in 
> code, then I don't
> think that it makes any sense to expect that Errors in general 
> will stay in
> production code. [...]

I personally think that, as a general rule, Errors should stay in 
production code.  I thought we had already separated 
-noboundscheck from -release, but I just tested now and that 
doesn't seem to be the case: -release still implies 
-noboundscheck.

D prides itself on being safer than C and C++, what with its 
default array bounds checks to combat buffer overruns and all, 
but as it turns out we're not that much better off.  The -release 
switch practically screams "use me in production code", but 
what's the point of bounds checking if it is only ever used while 
developers are testing their code?

Lars