what is up with this code?

auto t = tuple(1,'a',3.333,false);
pragma(msg,typeof(t.tupleof[2 .. $]).stringof);

spits out

(double, bool, int, char, double, bool)

> what is up with this code?
>
> auto t = tuple(1,'a',3.333,false);
> pragma(msg,typeof(t.tupleof[2 .. $]).stringof);
>
> spits out
>
> (double, bool, int, char, double, bool)


template Tuple(E...)
{
alias E Tuple;
}
alias Tuple!(1,'a',3.333,false) t;
pragma(msg,typeof(t.tupleof[2 .. $]).stringof);
//Error

pragma(msg,typeof(t[2..$].stringof);
//writes (double, bool)

On Fri, Jun 12, 2009 at 12:10 AM, Ellery Newcomer<ellery-newcomer@utulsa.edu> wrote:
> what is up with this code?
>
> auto t = tuple(1,'a',3.333,false);
> pragma(msg,typeof(t.tupleof[2 .. $]).stringof);
>
> spits out
>
> (double, bool, int, char, double, bool)
>

It has to do with the way Tuple is implemented in std.typecons:

    union
    {
        Types field;
        mixin(tupleFields!(0, T));
    }

"field" is of type (double, bool, int, char), and the mixin defines something like "struct { double _0; bool _1; int _2; char _3; }". Since it's a union, the field member overlaps with the anonymous struct, just giving you two different ways of accessing the same member: t.field[0] or t._0.

When DMD does the tupleof, it puts all the union members in the tuple, giving you what looks like a duplicated type list.

You can instead use:

	pragma(msg,typeof(t.field[$ - 2 .. $]).stringof);

On Fri, Jun 12, 2009 at 11:00 AM, Jarrett Billingsley<jarrett.billingsley@gmail.com> wrote:
> On Fri, Jun 12, 2009 at 12:10 AM, Ellery Newcomer<ellery-newcomer@utulsa.edu> wrote:
>> what is up with this code?
>>
>> auto t = tuple(1,'a',3.333,false);
>> pragma(msg,typeof(t.tupleof[2 .. $]).stringof);
>>
>> spits out
>>
>> (double, bool, int, char, double, bool)
>>
>
> It has to do with the way Tuple is implemented in std.typecons:
>
>    union
>    {
>        Types field;
>        mixin(tupleFields!(0, T));
>    }
>
> "field" is of type (double, bool, int, char), and the mixin defines something like "struct { double _0; bool _1; int _2; char _3; }". Since it's a union, the field member overlaps with the anonymous struct, just giving you two different ways of accessing the same member: t.field[0] or t._0.
>
> When DMD does the tupleof, it puts all the union members in the tuple, giving you what looks like a duplicated type list.
>
> You can instead use:
>
>        pragma(msg,typeof(t.field[$ - 2 .. $]).stringof);

Er,

	pragma(msg,typeof(t.field[2 .. $]).stringof);