• d-bugmail puremagic.com (50/53) Aug 21 2012 http://d.puremagic.com/issues/show_bug.cgi?id=8573

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=8573

           Summary: A simpler Phobos function that returns the index of
                    the mix or max item
           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



countUntil returns a signed value with the position, or -1 if not found:


import std.algorithm: countUntil;
void main() {
    assert(countUntil("hello world", 'r') == 8);
}


But to find the index of the minimum item things become more complex and more
bug-prone:

import std.algorithm: minPos;
import std.range: walkLength;
void main() {
    immutable s = "hello world";
    immutable sizediff_t mpos = s.walkLength() - minPos(s).walkLength();
    assert(mpos == 5);
}

I have typed mpos "sizediff_t" to avoid troubles caused by a unsigned position
value.


In Python taking the sum() of an empty list (array) returns 0, while searching
for min/max in an empty list causes a ValueError exception to be thrown:

 a = []
 sum(a)



0
 min(a)



Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: min() arg is an empty sequence


In D here mpos is 0:

import std.algorithm: minPos;
import std.range: walkLength;
void main() {
    immutable s = "";
    immutable sizediff_t mpos = s.walkLength() - minPos(s).walkLength();
    assert(mpos == 0);
}


So in Phobos I'd like a simple to use function that returns the sizediff_t
index of the min item (and when the input is empty, it returns -1 or throws an
exception).

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