[Issue 5530] New: std.algorithm.len()

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=5530

           Summary: std.algorithm.len()
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody at puremagic.com
        ReportedBy: bearophile_hugs at eml.cc


--- Comment #0 from bearophile_hugs at eml.cc 2011-02-05 17:22:30 PST ---
A simple task asks to sort an array according to the length of its items. This
is a D2 solution:


import std.stdio, std.algorithm;
void main() {
    auto l =
[['a','b','c'],['d','e'],['f','g','h'],['i','j','k','l'],['m','n'],['o']];
    schwartzSort!((s){return s.length; })(l);
    writeln(l);
}


It's supposed to print:
[['o'], ['d', 'e'], ['m', 'n'], ['a', 'b', 'c'], ['f', 'g', 'h'], ['i', 'j',
'k', 'l']]


I suggest to add a simple len() function to std.algorithm, that allows to
shorten that very common code (mapping lengths is a very common operation):

import std.stdio, std.algorithm;
size_t len(Range)(Range r) if (is(typeof(r.length))) {
    return r.length;
}
void main() {
    auto l =
[['a','b','c'],['d','e'],['f','g','h'],['i','j','k','l'],['m','n'],['o']];
    schwartzSort!len(l);
    writeln(l);
}


In Python the "len()" function is a free function to allow it to be used as
mapping function, sorting function for a Schwartz sort, etc. In Ruby there is a
"size" standard attribute, and blocks are more used.

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