• Ellery Newcomer <ellery-newcomer utulsa.edu> Jun 11 2009
• "Saaa" <empty needmail.com> Jun 11 2009
• Jarrett Billingsley <jarrett.billingsley gmail.com> Jun 12 2009
• Jarrett Billingsley <jarrett.billingsley gmail.com> Jun 12 2009

Ellery Newcomer <ellery-newcomer utulsa.edu> writes:

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)

"Saaa" <empty needmail.com> writes:

 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)

Jarrett Billingsley <jarrett.billingsley gmail.com> writes:

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);

Jarrett Billingsley <jarrett.billingsley gmail.com> writes:

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 =3D 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:

 =A0 =A0union
 =A0 =A0{
 =A0 =A0 =A0 =A0Types field;
 =A0 =A0 =A0 =A0mixin(tupleFields!(0, T));
 =A0 =A0}

 "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:

 =A0 =A0 =A0 =A0pragma(msg,typeof(t.field[$ - 2 .. $]).stringof);


Er,

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