On 08/17/2011 09:35 PM, 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.
The .. 'operator' is the operator with the lowest precedence in D (it
binds even less strongly than ?:), so there is no way auto a = 3 .. 5
can ever work without a breaking language change.
But again, 'case range:' matches 'range', not each individual element of
'range' so you'd actually still need a special range syntax for case
statements.
