Proposal: allow C++17 fold expressions

[Daniel Cheng]

Using fold expressions can avoid the need to write helpers to unpack the args one at a time.

For example, this:

#include <utility>

template <typename... Args>
int Sum(Args&&... args);

template <typename T, typename... Args>
int Sum(const T& val, Args&&... args) {
  return val + Sum(std::forward<Args>(args)...);
}

template <typename T>
int Sum(const T& val) {
  return val;
}

int main() {
  return Sum(1, 2, 3, 4);
}

Can be simplified into:

template <typename... Args>
int Sum(Args&&... args) {
  return (args + ...);
}

int main() {
  return Sum(1, 2, 3, 4);
}

One example where this helps can be found in https://chromium-review.googlesource.com/c/chromium/src/+/3709951/8..11.

Daniel

[dan...@chromium.org]

LGTM

--
You received this message because you are subscribed to the Google Groups "cxx" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cxx+uns...@chromium.org.
To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/cxx/CAF3XrKo8Wr_wzwYdvcn-mTtqZPpQ75vEO%2BsYkLdZoM9djDoOpg%40mail.gmail.com.

[Kyle Charbonneau]

+1, the second snippet of code is much easier to understand.

To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/cxx/CAHtyhaQGXFnusK0SxKBBS7A%2B7BAAZHtf8YJjQi7Z4w7nJ8JUvQ%40mail.gmail.com.

[Anton Bikineev]

+1 (I already used them in a test, wrongly assuming they were allowed :) )

To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/cxx/CAERSRDCd4nNbjfL-Ku4iXMwx4qv5fcSPxmhxRdsbyAiftRvB9A%40mail.gmail.com.

[Roland Bock]

+1 for allowing fold expressions.

Awesome for avoiding recursion in TMP.

On Tue, Jul 5, 2022 at 3:50 PM Kyle Charbonneau <kyle...@chromium.org> wrote:

To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/cxx/CAERSRDCd4nNbjfL-Ku4iXMwx4qv5fcSPxmhxRdsbyAiftRvB9A%40mail.gmail.com.

--

--

Roland Bock

Software Engineering Manager

rb...@google.com

Google Germany GmbH

Erika-Mann-Straße 33

80636 München

Geschäftsführer: Paul Manicle, Liana Sebastian

Registergericht und -nummer: Hamburg, HRB 86891

Sitz der Gesellschaft: Hamburg

This e-mail is confidential. If you received this communication by mistake, please don't forward it to anyone else, please erase all copies and attachments, and please let me know that it has gone to the wrong person.

The above terms reflect a potential business arrangement, are provided solely as a basis for further discussion, and are not intended to be and do not constitute a legally binding obligation. No legally binding obligations will be created, implied, or inferred until an agreement in final form is executed in writing by all parties involved.

[Daniel Cheng]

This seems fairly non-controversial, so https://chromium-review.googlesource.com/c/chromium/src/+/3746805.

Daniel

[Mark Mentovai]

I endorse this too, but maybe give it another day for opinions to trickle in, so that this isn’t opened and driven entirely to completion entirely within a holiday weekend in the US.

Mark

To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/cxx/CAF3XrKrFs2%2BOd4v%3Dn6yx8nv8q7zU660ED1whP2CYFdC7HDJDWA%40mail.gmail.com.

[Avi Drissman]

I think this is good as well, but +1 to waiting a day or two more.

To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/cxx/CAHk1GDxCfOuwsNg6dw1dOJuJWLypiB7Gf%2BNdM8Wp_mdq6EgG9g%40mail.gmail.com.

[Daniel Cheng]

I'm going to go ahead and submit, since there hasn't been any further feedback that we should not allow this (and all the previous responses were positive).

Daniel