DIP33: A standard exception hierarchy

[Lars T. Kyllingstad]

On Wednesday, 3 April 2013 at 15:29:01 UTC, deadalnix wrote:
> On Wednesday, 3 April 2013 at 09:40:27 UTC, Lars T. Kyllingstad 
> wrote:
>> For arrays, RangeError is synonymous with "out of bounds".  I 
>> see no reason to invent a new class just for this purpose.
>>
>
> Exactly, no need for RangeError (as out of bound access can be 
> produced in many situation that don't involve ranges).

Well the word "range" has two meanings here:  One is the 
programming language concept, i.e. a type that defines empty, 
front, etc.  The other is the English word for which Google 
offers the following definition: "The area of variation between 
upper and lower limits on a particular scale."  In light of this, 
I don't think RangeError is a bad name for an array bounds 
violation.


>> And note that I'm not saying that ranges should be restricted 
>> to *only* throwing RangeErrors.  Generally, it should be used 
>> in situations that are analogous to out of bounds for arrays, 
>> such as trying to pop past the end of the range.
>>
>
> The data always come from somewhere. That somewhere can't 
> provide anymore data for a reason. Because you reached the end 
> of a file (IOException or something) because the network 
> disconnected (NetworkException) or whatever.
>
> RangeError imply that the data magically appears from a range, 
> without any actual source, which is impossible.

Of course it's not impossible.

std.range.iota
std.range.recurrence
std.range.sequence

>> However, some ranges may want to do something else in this 
>> situation.  An output range that writes to a file, for 
>> instance, may want to throw a "disk full" exception.  A 
>> wrapper range may simply propagate any errors from the 
>> underlying range.
>>
>
> Exactly. In general, wrapper should simply forward calls and 
> let the source fail when its own logic isn't involved.

This is not always possible or convenient.  Assume the directory 
"foo" contains 4 files.

     auto fourFiles = std.file.dirEntries("foo", SpanMode.shallow);
     auto twoFiles = std.range.take(fourFiles, 2);
     twoFiles.popFront();
     twoFiles.popFront();
     twoFiles.popFront();

Which exception should the last popFront() throw?

Lars