Can you zip with the new ranges library?

Question

Given two C++2a ranges (as in objects that conform to the ranges concept of the ranges library) a and b, of equal length, is there a way to zip them together such that:

for (const auto& [a,b] : zip(a,b))

does what you expect? That is, it returns a range that has something destructurable binding pairs:

(a.begin(), b.begin())
(a.begin()+1, b.begin()+1)
(a.begin()+2, b.begin()+2)
...
(a.end()-1, b.end()-1)

_Zip_ what please?? Post a self contained question as required. — πάντα ῥεῖ, Feb 15 '19 at 20:57
You mean something like Python [`zip`](https://docs.python.org/3.5/library/functions.html#zip)? — Yksisarvinen, Feb 15 '19 at 20:59

Barry · Accepted Answer · 2021-06-04T14:05:10.240

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As you can see, there is no zip_view currently in C++20 (as of this writing).

It was being proposed in P1035R4 (along with a handful of other adapters), the previous version of which was favorable received in San Diego and seemed like it has a very reasonable chance of landing in C++20. There are open questions regarding proxy references, but I don't think that's specific to zip.

Those questions regarding proxy references ended up causing zip to get dropped from P1035 and it was not adopted for C++20. Instead, zip is being proposed for C++23 as part of P2321 (which additionally includes a description of the kinds of proxy reference changes I mentioned).

edited Jun 04 '21 at 14:05

answered Feb 15 '19 at 21:18

Barry

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Why is the example `for (auto xy = view::zip(x, y); auto [xi, yi] : xy)` and not `for (auto [xi, xi] : xy)` ? – Andrew Tomazos Feb 15 '19 at 21:26
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@AndrewTomazos You mean why isn't it `for (auto [xi, yi] : view::zip(x, y))`? Just a matter of taste, the two are equivalent. – Barry Feb 15 '19 at 21:38
Barry maybe update the answer to say that planned standard is now C++23 – NoSenseEtAl Jun 04 '21 at 12:41

score 0 · Answer 2 · answered Feb 15 '19 at 21:54

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ranges v3 niebler has already made public a library with a lazy zip and some more general forms also zip_view and others. Implemented as a header only library so you can read the code. With some nice examples of uses. In c++ zip will probably return a tuple when asked. and indexing into that tuple will give you the values.

answered Feb 15 '19 at 21:54

Mellester

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Yes, `range-v3` is what `std` ranges in C++20 is based on... but it hasn't (yet) migrated `zip`. – underscore_d Aug 25 '20 at 11:17

Can you zip with the new ranges library?

2 Answers2