How is `auto` and not `alias` appropriate for alias sequences?

[ZombineDev via Digitalmars-d]

On Friday, 11 December 2015 at 14:12:16 UTC, ZombineDev wrote:
> [...]

In short, the current D terminology calls:
compile-time lists -> AliasSeq 
(http://dlang.org/phobos/std_meta#AliasSeq)
run-time values of type lists -> Tuple 
(http://dlang.org/phobos/std_typecons#.Tuple)

Another example:

Tuple!(int, string)(3, "apples") obj;

obj is a run-time tuple of the integer 3 and the string "apples".

The template arguments int and string are a type list (and a 
special case of an alias sequence).

alias Point2D = Tuple!(int, "x", int, "" ~ 'y');

auto point_a = Point2D(3, 4);
auto point_b = Point2D(1, -7);

Point2D is an alias to the type Tuple!(int, "x", int, "" ~ 'y'), 
which is a template instance of the Tuple(Specs...) template.

The (int, "x", int, "" ~ 'y') template arguments have both types 
and compile-time expressions among them and that's why we call it 
an alias sequence and not just a type list.

point_a and point_b are tuples of two ints and are run-time 
values.

You can put the template arguments used for Point2D in a AliasSeq:

alias Point3DTemplateArgs = AliasSeq!(float, "x", int, "y", 
double, "z");

And you can use those template args to make a new instance of the 
Tuple template:

alias Point3D = Tuple!(Point3DTemplateArgs);

Some runtime values can also be computed at compile-time and you 
can use them for enums.

http://dpaste.dzfl.pl/a05cf181331d (I think that only the output 
of "2:" is inconsistent.)

Also I found this article, which maybe helpful: 
http://dlang.org/ctarguments.html