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digitalmars.D.bugs - [Issue 4582] New: distinct field names constraint for std.typecons.Tuple

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4582

           Summary: distinct field names constraint for std.typecons.Tuple
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: patch
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc


--- Comment #0 from bearophile_hugs eml.cc 2010-08-04 17:21:25 PDT ---
It's better to put guards as template constraints at the std.typecons.Tuple, so
erroneous Tuple template instantiations fail at the instantiation point, giving
a more useful error message in the user code instead giving an error inside the
std.typecons module (this is one of the main purposes of template constraints).

This code guards against duplicated field names:


private template Iota(int stop) { // this is useful in general
    static if (stop <= 0)
        alias TypeTuple!() Iota;
    else
        alias TypeTuple!(Iota!(stop-1), stop-1) Iota;
}

private bool distinctFieldNames(T...)() {
    enum int tlen = T.length; // can't move this below, probably DMD bug
    foreach (i1; Iota!(tlen))
        static if (is(typeof(T[i1]) : string))
            foreach (i2; Iota!(tlen))
                static if (i1 != i2 && is(typeof(T[i2]) : string))
                    if (T[i1] == T[i2])
                        return false;
    return true;
}

// ...............

struct Tuple(T...) if (distinctFieldNames!(T)())
{

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4582


Andrei Alexandrescu <andrei metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |andrei metalanguage.com
         AssignedTo|nobody puremagic.com        |andrei metalanguage.com


--- Comment #1 from Andrei Alexandrescu <andrei metalanguage.com> 2010-10-07
08:02:31 PDT ---
Excellent.

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prev sibling parent d-bugmail puremagic.com writes:
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--- Comment #2 from bearophile_hugs eml.cc 2010-10-07 13:25:43 PDT ---
Thank you. But I think some tests/benchmarks may be done to make sure this
extra test doesn't slow down too much the compilation of programs that define
many tuple types.

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