[Issue 7484] New: std.algorithm.copy overlapping array copy

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http://d.puremagic.com/issues/show_bug.cgi?id=7484

           Summary: std.algorithm.copy overlapping array copy
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody at puremagic.com
        ReportedBy: ellery-newcomer at utulsa.edu


--- Comment #0 from Ellery Newcomer <ellery-newcomer at utulsa.edu> 2012-02-11 11:52:25 PST ---
Way back in 2.054 you could use std.algorithm.copy in an overlapping copy,
e.g.,

copy(a[5 .. 10], a[4 .. 9]);

Fast forward a couple releases, and copy seems to be delegating to

a[4 .. 9] = a[5 .. 10];

in the interest of speed, but here overlapping copy is prohibited by spec and
implementation.

I maintain that std.algorithm.copy should permit overlapping copy in the case
of arrays because

1: it is consistent with STL copy's semantics (see Note 2)

2: copy can still do an overlapping copy on non-array range types*, and failing
to do so on arrays is an inconsistency

If this behavior is desired, the docs should at least make mention of it. Also
note that if copy's behavior is reverted, it could be the solution for issue
1317.

*proof:

auto a = make!(SList!int) ([1,2,3,4,5,6,7,8,9,10]);
auto r1 = a[];
auto r2 = a[];
r2.popFront();
copy(r2,r1);
writeln(a[]); // prints [2, 3, 4, 5, 6, 7, 8, 9, 10, 10]

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