Switch: Case Range Syntax

[Jacob Carlborg]

On 2011-08-17 22:00, Jonathan M Davis wrote:
> On Wednesday, August 17, 2011 12:35 Jacob Carlborg wrote:
>> On 2011-08-17 19:48, Jonathan M Davis wrote:
>>> On Wednesday, August 17, 2011 10:27 Vijay Nayar wrote:
>>>> D adds a very handy feature that allows you to check for a range of
>>>> values in a single case. Is there a particular reason that the syntax
>>>> "case<start>: .. case<end>:" is used instead of treating the case
>>>> statement similarly to an array slice, e.g. "case<start>  ..<end>:"?
>>>>
>>>> For example:
>>>>
>>>> import std.stdio;
>>>>
>>>> void main() {
>>>> int bob = 12;
>>>> switch (bob) {
>>>> // Why not "case 0 .. 9:"?
>>>> case 0: .. case 9:
>>>> writeln("Less than 10.");
>>>> case 10: .. case 19:
>>>> writeln("Less than 20.");
>>>> case 20: .. case 29:
>>>> writeln("Less than 30.");
>>>> break;
>>>> default:
>>>> break;
>>>> }
>>>> // Output: Less than 20. Less than 30.
>>>> }
>>>
>>> I don't know, but ranged case statements don't have the same semantics as
>>> giving a range of values when slicing or to a foreach loop, so that may
>>> be why.
>>>
>>> arr[0 .. 10]
>>>
>>> does _not_ include the element at index 10.
>>>
>>> case 0: case 10:
>>>
>>> _does_ include 10. So, it actually probably be a bad thing for them to
>>> use the same syntax. To use the same syntax for both would make the
>>> semantics of that syntax inconsistent and confusing.
>>>
>>> - Jonathan M Davis
>>
>> D should have a built-in range type. One that supports syntax for both
>> including and excluding the last element:
>>
>> auto a = 3 .. 5
>> auto b = 3 ... 5
>>
>> Then we wouldn't need a special range syntax for switch statements. You
>> could store ranges in variables and pass them to functions. opSlice
>> probably wouldn't be needed, instead opIndex could be used and you would
>> declare the method to take a range instead of two integers.
>
> I suggest that you read the thread that Lars linked to. That type of syntax
> got shot down essentially for being too easy to confuse .. with ... making it
> hard to read and easy to screw-up. Regardless, the whole issue got discussed
> ad naseum there, and the situation definitely isn't going to change for D2, so
> there really isn't much point in arguing the pros and cons at this point.
> Maybe there will be something similar in D3 if someone can find an
> appropriately clear syntax for it, but I'd be very surprised if any such thing
> happened in D2.
>
> - Jonathan M Davis

Yes I know that it has been discussed before. We don't have to discuss 
this again, I'm just telling my opinion and I don't agree with .. and 
... being confusing.

-- 
/Jacob Carlborg