http://d.puremagic.com/issues/show_bug.cgi?id=10543

           Summary: std.algorithm.map incorrectly uses source range length
                    for narrow strings
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: peter.alexander.au@gmail.com


--- Comment #0 from Peter Alexander <peter.alexander.au@gmail.com> 2013-07-04 09:30:32 PDT ---
void main()
{
    import std.algorithm;
    import std.stdio;
    string s = "こんにちは世界";
    auto m = s.map!(a => 1);
    writeln(m, ", ", m.length);
}

Gives:

[1, 1, 1, 1, 1, 1, 1], 21

Clearly the reported length (21) is wrong, it should be 7.

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--- Comment #1 from Peter Alexander <peter.alexander.au@gmail.com> 2013-07-04 09:31:54 PDT ---
(In reply to comment #0)
> Clearly the reported length (21) is wrong, it should be 7.

Scratch that. length shouldn't be available at all for narrow strings as it is unobtainable in constant time.

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bearophile_hugs@eml.cc changed:

           What    |Removed                     |Added
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                 CC|                            |bearophile_hugs@eml.cc


--- Comment #2 from bearophile_hugs@eml.cc 2013-07-04 10:41:41 PDT ---
Where's the bug here?

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--- Comment #3 from Peter Alexander <peter.alexander.au@gmail.com> 2013-07-04 10:43:22 PDT ---
(In reply to comment #2)
> Where's the bug here?

It says the length of [1, 1, 1, 1, 1, 1, 1] is 21. It isn't. It's 7.

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9999 <mailnew4ster@gmail.com> changed:

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                 CC|                            |mailnew4ster@gmail.com


--- Comment #4 from 9999 <mailnew4ster@gmail.com> 2013-07-04 10:47:52 PDT ---
21 is the number of UTF-8 code units.
Using dstring produces 7.

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--- Comment #5 from Peter Alexander <peter.alexander.au@gmail.com> 2013-07-04 10:54:42 PDT ---
(In reply to comment #4)
> 21 is the number of UTF-8 code units.
> Using dstring produces 7.

I am not requesting the length of the string, I am requesting the length of the map over the string. As ranges, strings are ranges of code points, not code units, so the number of elements in the *map* (confirmed by the output) is seven, i.e. that is the number of times you can safely call popFront on the map.

I'm struggling to understand the confusion.

m is a range of seven integers
m.length is 21
walkLength(m) is also 21

This is completely broken.

I fully understand that narrow strings use length to report code units, not code points, but m is not a string, so that distinction does not apply.

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monarchdodra@gmail.com changed:

           What    |Removed                     |Added
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                 CC|                            |monarchdodra@gmail.com


--- Comment #6 from monarchdodra@gmail.com 2013-07-04 12:51:16 PDT ---
(In reply to comment #5)
> I'm struggling to understand the confusion.

The problem is perfectly clear.

Are you already correcting this? If not, I'll take care of it.

I remember having seen this in one of my first pulls correcting map, but got confused about the fact there is an *explicit* test to do things wrong... Time to correct it for good I guess.

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--- Comment #7 from Peter Alexander <peter.alexander.au@gmail.com> 2013-07-04 13:15:10 PDT ---
(In reply to comment #6)
> (In reply to comment #5)
> > I'm struggling to understand the confusion.
> 
> The problem is perfectly clear.
> 
> Are you already correcting this? If not, I'll take care of it.
> 
> I remember having seen this in one of my first pulls correcting map, but got confused about the fact there is an *explicit* test to do things wrong... Time to correct it for good I guess.

I'm not fixing it right now, go ahead.

I only noticed it when I looked at the source. No idea why it's explicitly coded to be wrong...

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monarchdodra@gmail.com changed:

           What    |Removed                     |Added
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           Keywords|                            |accepts-invalid
             Status|NEW                         |ASSIGNED
         AssignedTo|nobody@puremagic.com        |monarchdodra@gmail.com


--- Comment #8 from monarchdodra@gmail.com 2013-07-05 05:49:13 PDT ---
https://github.com/D-Programming-Language/phobos/pull/1389

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--- Comment #9 from github-bugzilla@puremagic.com 2013-07-06 02:24:49 PDT ---
Commits pushed to master at https://github.com/D-Programming-Language/phobos

https://github.com/D-Programming-Language/phobos/commit/0a710876007bf8509d4f62453311e0bb6adbc7ca
Fix Issue 10543 - std.algorithm.map incorrectly uses source range length for
narrow strings

Strange, because there was an explicit override for strings to forward length.

In any case, this is now fixed.

https://github.com/D-Programming-Language/phobos/commit/201edf4c8055ca0ac0079b9a8b711b68668c7974 Merge pull request #1389 from monarchdodra/mapString

Fix Issue 10543 - std.algorithm.map incorrectly uses source range length...

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