Tuple DIP

[Manu]

On 12 January 2018 at 14:44, Timon Gehr via Digitalmars-d <
digitalmars-d at puremagic.com> wrote:

> As promised [1], I have started setting up a DIP to improve tuple
> ergonomics in D:
>
> https://github.com/tgehr/DIPs/blob/tuple-syntax/DIPs/DIP1xxx-tg.md
>
>
> This DIP aims to make code like the following valid D:
>
> ---
> auto (a, b) = (1, 2);
> (int a, int b) = (1, 2);
> ---
>
> ---
> foreach((sum, diff); [(1, 2), (4, 3)].map!((a, b) => (a + b, a - b)))
> {
>     writeln(sum, " ", diff);
> }
> /+ prints:
> 3 -1
> 7 1
> +/
> ---
>
> Before going ahead with it, I'd like some preliminary community input:
>
> - I'm not yet completely satisfied with the DIP.
>   (See section "Limitations".)
>   Please let me know suggestions or further concerns you might have.
>
>
> - There are good example use cases missing. While I'm confident I could
>   invent a few of them given a little time, I thought maybe I can
>   expedite the process and make the point more convincingly by asking
>   for use cases you encountered in your own code. The DIP already
>   contains an example due to bearophile.
>
>
> [1] https://forum.dlang.org/post/or625h$2hns$1@digitalmars.com
>


This is nice work!
I hope this is seriously considered.

I'll add my 2c...
You discuss 'auto unpacking', can you justify the value of this?

I quite like C++ explicit unpacking (using ...), and I wouldn't be upset to
see that appear here too.
Explicit unpacking would solve your breaking change with auto unpacking,
but the buggest advantage of C++'s '...' statement is that the unpack can
involve expressions.
  auto t = (1, 2, 3);
  f(t...);          // <-- regular expansion: f(1, 2, 3);
  f(arr[t]...);    // <-- expression expansion: f(arr[1], arr[2], arr[3]);
etc...

It's amazingly useful to perform tuple expansion on an expression involving
the tuple!

So, why might implicit expansion be preferred to explicit expansion?
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