Switch: Case Range Syntax

[Jacob Carlborg]

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.

-- 
/Jacob Carlborg