Places a TypeTuple can be used

[Dicebot]

On Friday, 16 August 2013 at 15:40:35 UTC, Ali Çehreli wrote:
> Exactly. Only then this concept would be easy to understand and 
> explain. It would make "a comma-separated list of 
> expressions/types" a language construct. Done.

It does complicate things that sometimes TypeTuple is accepted in 
cases where comma-separated list does not:

import std.typetuple;

void main()
{
     //alias TT = TypeTuple!(int, string);
     //TT twoVars;
     (int, string) twoVars; // do you expect this to work?
     static assert(is(typeof(twoVars[0]) == int));
     static assert(is(typeof(twoVars[1]) == string));
}

The fact that built-in concept of tuple can't be expressed with 
built-in syntax creates lot of learning issues. In that regard, 
defining "list of expressions/types" as language construct goes 
as a solution both ways.

I honestly think it is one of the cases where idea "wow, we can 
have library support for type tuples instead of language 
support!" has failed with an enormous technical debt.