Bug 9447 – iota should generate char intervals too
Status
RESOLVED
Resolution
FIXED
Severity
enhancement
Priority
P2
Component
phobos
Product
D
Version
D2
Platform
All
OS
All
Creation time
2013-02-03T18:05:18Z
Last change time
2020-03-21T03:56:37Z
Keywords
rejects-valid
Assigned to
No Owner
Creator
bearophile_hugs
Comments
Comment #0 by bearophile_hugs — 2013-02-03T18:05:18Z
Spinoff of Issue 8920
import std.range: iota;
void main() {
foreach (i; iota('a', 'f')) {}
}
DMD 2.062alpha gives:
temp.d(3): Error: template std.range.iota does not match any function template declaration. Candidates are:
...\dmd2\src\phobos\std\range.d(5107): std.range.iota(B, E, S)(B begin, E end, S step) if ((isIntegral!(CommonType!(B, E)) || isPointer!(CommonType!(B, E))) && isIntegral!(S))
...\dmd2\src\phobos\std\range.d(5192): std.range.iota(B, E)(B begin, E end) if (isFloatingPoint!(CommonType!(B, E)))
...\dmd2\src\phobos\std\range.d(5199): std.range.iota(B, E)(B begin, E end) if (isIntegral!(CommonType!(B, E)) || isPointer!(CommonType!(B, E)))
...\dmd2\src\phobos\std\range.d(5260): std.range.iota(E)(E end)
...\dmd2\src\phobos\std\range.d(5267): std.range.iota(B, E, S)(B begin, E end, S step) if (isFloatingPoint!(CommonType!(B, E, S)))
temp.d(3): ... (1 more, -v to show) ...
...\dmd2\src\phobos\std\range.d(5107): Error: template std.range.iota cannot deduce template function from argument types !()(char,char)
Comment #1 by andrej.mitrovich — 2013-02-04T10:15:42Z
The reason I mentioned Unicode in Issue 8920 is because I'm unsure whether simply incrementing the integral value of a character will produce a valid character (valid in how the Unicode standard defines it).
For ASCII 'a'--'z' it's likely not an issue, but I'm thinking about the case of wchars and dchars. E.g. we would probably have to use isValidDchar.
Comment #2 by issues.dlang — 2013-02-04T10:48:33Z
It is definitely _not_ the case that adding 1 to a wchar or dchar will necessarily result in a valid value. In both of them, there's a block in the middle which is invalid. Just like at the implementation of isValidDchar.
Comment #3 by andrej.mitrovich — 2013-02-04T10:57:34Z
(In reply to comment #2)
> It is definitely _not_ the case that adding 1 to a wchar or dchar will
> necessarily result in a valid value. In both of them, there's a block in the
> middle which is invalid. Just like at the implementation of isValidDchar.
Is this the only restriction though? If that's so, it should be easy to implement this feature with a single runtime check to verify the range doesn't go over the invalid block.
Comment #4 by monarchdodra — 2013-07-26T00:12:08Z
(In reply to comment #3)
> (In reply to comment #2)
> > It is definitely _not_ the case that adding 1 to a wchar or dchar will
> > necessarily result in a valid value. In both of them, there's a block in the
> > middle which is invalid. Just like at the implementation of isValidDchar.
>
> Is this the only restriction though? If that's so, it should be easy to
> implement this feature with a single runtime check to verify the range doesn't
> go over the invalid block.
I think that is a bad idea. We should keep it simple: User asks to iterate over xchars of values low to high, and that is all we should return.
When it comes to wchars or dchars, the notion of "invalid" is really in the eye of the beholder anyway.