Tuple/TypeTuple etc.

[John Colvin]

On Saturday, 17 August 2013 at 01:01:10 UTC, Dicebot wrote:
> Currently it is not the case. typeof(tuple(1,2)) is 
> Tuple!(int,int), not TypeTuple!(int, int). But 
> typeof(TypeTuple(1,2)) is TypeTyple!(int, int) :)

Whu?

There is no such type as TypeTuple!(int, int), it is completely 
aliased away to a builtin tuple.

Also, printing out types is actually rather misleading, as it 
chooses when to use or not use tuple() in annoying ways e.g. 
TypeTuple!(int, string) is (int, string) but TypeTuple!(int, 3) 
is tuple(int, 3)   Either they are both tuples, or neither is.

To the best of my knowledge, there is only this:

1) collections of items, called tuples. They can contain pretty 
much anything you want, as long it's available at compile-time.
They are ***not types***. If and only if a tuple contains only 
types, the tuple itself is a type. This is often referred to as a 
type-tuple. In current D, tuples of all varieties are created by 
variadic template parameters.*

2) instantiations of type-tuples. These are a collection of 
runtime values, individually accessible by indexing or foreach 
iteration. std.typecons.Tuple is a wrapper around one of these 
providing some extra functionality.

*std.typetuple.TypeTuple only exists to provide convenient syntax 
for this.