DIP33: A standard exception hierarchy

[Lars T. Kyllingstad]

On Tuesday, 2 April 2013 at 10:37:08 UTC, deadalnix wrote:
> On Monday, 1 April 2013 at 11:08:16 UTC, Lars T. Kyllingstad 
> wrote:
>> It's time to clean up this mess.
>>
>> http://wiki.dlang.org/DIP33
>
> Several things.
>
> First the usage of enums isn't the right path. This makes it 
> hard to extend in general, and it is a poor man replacement for 
> sub classes in general.

Phobos/druntime devs can always add to the enums.  Users still 
have the option of subclassing if strictly necessary.


> As a rule of thumb, when you use switch in OOP code, you are 
> likely to do something wrong.

I'm not sure I agree with that rule.  And anyway, D's final 
switch mitigate some of the problems with classic switch.

> Second, many of you error are recoverable here. It isn't quite 
> satisfying.
>
> RangeError is a very bad thing IMO. It completely hides why the 
> range fails in the first place. Trying to access front when not 
> possible for instance, is an error for a reason (which is range 
> dependent). That reason must be the source of the 
> error/exception.

No.  To call front on an empty range is a programming error, 
plain and simple.  It's like trying to access the first element 
of an empty array.  The fact that some ranges may allow it anyway 
does not change anything.


> In general the hierarchy is weird. Why isn't 
> NetworkingException (why not NetworkException ?) a subclass of 
> IOException ?

Because they are supposed to signal different error conditions.


> OutOfMemoryError on its own isn't good IMO. The Error hierarchy 
> is made for error that aren't recoverable (or may not be 
> recoverable). It include a whole class of problem, and OOM is 
> only one of them (another example is Stack overflow errors).

The DIP sort of redefines Error to mean "programming error".

Lars