http://d.puremagic.com/issues/show_bug.cgi?id=8467

           Summary: A different third signature for std.algorithm.count
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2012-07-29 19:33:55 PDT ---
The third signature of std.algorithm.count() is:
http://dlang.org/phobos/std_algorithm.html#count

size_t count(alias pred = "true", Range)(Range r);


So this program is equivalent to using walkLength, and in my opinion this is not so useful:

import std.algorithm: count;
void main() {
    assert(count([0, 0, 1]) == 3);
}


I think a more useful default for that third form is something similar to:

size_t count(alias pred = "a", Range)(Range r);


So it counts the true values:

import std.algorithm: count;
void main() {
    assert(count([0, 0, 1]) == 1);
}


But keep in mind that unlike Python in D even empty arrays are sometimes "true", etc:

import std.algorithm: count;
void main() {
    assert(count!"a"([(new int[1])[0..0]]) == 1);
}

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Andrei Alexandrescu <andrei@metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |andrei@metalanguage.com
         Resolution|                            |WONTFIX


--- Comment #1 from Andrei Alexandrescu <andrei@metalanguage.com> 2012-07-30 04:31:15 PDT ---
Nice idea, but breaks existing code.

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--- Comment #2 from bearophile_hugs@eml.cc 2012-07-30 09:09:08 PDT ---
(In reply to comment #1)
> Nice idea, but breaks existing code.

Thank you for the answer.

I think around there isn't much code uses that count() with no argument for its template, so not a lot of code is broken by this change.

If you are not interested in this enhancement, then I have opened a related enhancement request, Issue 8472

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