[Issue 4761] New: std.array.mul()

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=4761

           Summary: std.array.mul()
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: patch
          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 2010-08-29 15:31:21 PDT ---
In Python I use very often the * (__mul__) list operator, it's handy in many
situations (it is not lazy):

>>> "abc" * -1
''
>>> "abc" * 0
''
>>> "abc" * 1
'abc'
>>> "abc" * 5
'abcabcabcabcabc'
>>> [0] * 5
[0, 0, 0, 0, 0]


It's not a good idea to add a similar product operator to D arrays because
despite vector mult operation will probably require [] (while the mul doesn't
require it), the two are too much syntactically close, they risk being too much
bug-prone.

So I suggest to simply add this mul() to std.array (this must be eager, not a
lazy range, otherwise it's not handy for its purposes):


/// ...
T[] mul(T)(T[] items, int times) {
    T[] result;

    static if(!is( typeof(items) == void[] )) {
        if (times > 0 && items.length > 0) {
            if (items.length == 1) {
                result.length = times;
                result[] = items[0];
            } else {
                result.length = items.length * times;
                for (size_t pos; pos < result.length; pos += items.length)
                    result[pos .. pos+items.length] = items;
            }
        }
    }

    return result;
}

// demo ----------
import std.stdio;
void main() {
    auto a1 = [0].mul(10);
    writeln(a1);
    auto a2 = [0, 5, 10].mul(4);
    writeln(a2);
}


More unittests and a ddoct on request.

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