Why TypeTuple can be assigned to a variable

[Simen Kjaeraas]

On Wed, 12 Jun 2013 10:01:59 +0200, Zhenya <zheny at list.ru> wrote:

> Hi!
>
> I was just surprised when realized, that this code compiles and runs:
>
> import std.typetuple;
> import std.stdio;
>
> void main()
> {
>   auto foo = TypeTuple!("foo","bar");
> writeln(typeid(typeof(foo)));
>   writeln(foo);
> }
>
> If I were compiler expert,I'd say that it's a bug.But I am not)
> So, can anybody explain why it's work?

It is the equivalent of:

   TypeTuple!(string, string) foo;
   foo[0] = "foo";
   foo[1] = "bar";

The ability to have a tupetuple as a variable is very useful - if that
had not been possible one would need something akin to this:

struct Tuple(T...) {
     T[0] head;
     static if (T.length) {
         Tuple!(T[1..$]) tail;
     }
}

And to access the third element of a tuple one'd need to write:

     myTuple.tail.tail.head = "foo";

Clearly this is suboptimal, so D has better ways of doing such things.

-- 
Simen