http://d.puremagic.com/issues/show_bug.cgi?id=9447

           Summary: iota should generate char intervals too
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: rejects-valid
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2013-02-03 18:05:18 PST ---
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)

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Andrej Mitrovic <andrej.mitrovich@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |andrej.mitrovich@gmail.com


--- Comment #1 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2013-02-04 10:15:42 PST ---
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.

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Jonathan M Davis <jmdavisProg@gmx.com> changed:

           What    |Removed                     |Added
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                 CC|                            |jmdavisProg@gmx.com


--- Comment #2 from Jonathan M Davis <jmdavisProg@gmx.com> 2013-02-04 10:48:33 PST ---
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.

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--- Comment #3 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2013-02-04 10:57:34 PST ---
(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.

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monarchdodra@gmail.com changed:

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                 CC|                            |monarchdodra@gmail.com


--- Comment #4 from monarchdodra@gmail.com 2013-07-26 00:12:08 PDT ---
(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.

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