Tuple DIP

[Martin Nowak]

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On 01/12/2018 11:44 PM, Timon Gehr 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

Pardon me if things have been said already, can't really read through
all the thread.

- - Regarding underscore as placeholder.

https://issues.dlang.org/show_bug.cgi?id=13522

- - Regarding the "limitation"

Maybe you want some auto-packing feature there? Doesn't seem too bad,
we could come up with sth. when this turns out to become a common
nuisance.
Have you considered to lower (1, 2, 3)[0 .. 2] to tuple(tuple(1, 2,
3)[0 .. 2]) or using a non-std.typecons tuple where slicing does not
expand?

- - closed tuples?

The reference to std.typecons.tuple implies contiguous struct memory
layout (closed tuples).
This is a bit subtle for unpacking assignments which lower to

AliasSeq!(x, y) = tuple(y, x)[];

so on the left-hand side of an assignment, the syntax refers to a
non-contiguous (open) tuple.

Declarations like

auto (a, b) = (1, 2);

also seem to declare an open tuple (non-contiguous memory).

I assume that unpacking function arguments behaves similarly, i.e. on
ABI level, each argument is passed separately.


Overall looks really good. I think that would make for a great
addition to the language.

- -Martin
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