[R-pkg-devel] Native pipe in package examples

[Henrik Bengtsson]

On Thu, Jan 25, 2024 at 7:48 AM Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
>
> On 25/01/2024 10:27 a.m., Josiah Parry wrote:
> > Hey all,
> >
> > I've encountered use of the native pipe operator in the examples for
> > 'httr2' e.g.
> >
> > request("http://example.com") |> req_dry_run()
> >
> >
> > Since r-oldrel (according to rversions::r_oldrel()) is now 4.2.3, can the
> > native pipe be used in example code?
> >
> > I do notice that the package httr2 requires R >= 3.6.0 which implies that
> > the code itself does not use the native pipe, but the examples do.
>
> I think that the package should state it requires R (>= 4.1.0), since
> that code won't work in earlier versions.
>
> I believe it's a syntax error before 4.1.0, but don't have a copy handy
> to test.

Yes, support for the |> syntax was introduced in R 4.1.0;

$ Rscript --vanilla -e "getRversion()" -e "1:10 |> sum()"
[1] ‘4.0.5’
Error: unexpected '>' in "1:10 |>"
Execution halted

$ Rscript --vanilla -e "getRversion()" -e "1:10 |> sum()"
[1] ‘4.1.0’
[1] 55

> That means the package won't pass R CMD check in those old
> versions.  If it wasn't a syntax error, just a case of using a new
> feature, then I think it would be fine to put in a run-time test of the
> R version to skip code that won't run properly.

There's also the distinction of package code versus code in
documentation. If it's only example code in help pages that use the
native pipe, but the code in R/*.R does not, then the package will
still install and work with R (< 4.1.0).  The only thing that won't
work is when the user tries to run the code in the documented
examples.  I'd argue that it's okay to specify, say, R (>= 3.6.0) in
such an example.  It allows users with older versions to still use the
package, while already now migrating the documentation to use newer
syntax.

/Henrik
>
> Duncan Murdoch
>
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