R devel - Jun 2025 - Specifying a long string literal across several lines

Tomas,

Here is a good example of where this functionality would be useful:
https://github.com/R-ArcGIS/arcgislayers/blob/2b29f4c254e7e5a1dadce8d4b0015a70dfae39d4/R/arc-open.R#L19-L56

In order to prevent R CMD check notes I have to use `paste0()` to
concatenate long URLs. If we were able to use `\` to
separate the string across multiple lines, it would make the solution much
nicer!

On Mon, Jun 2, 2025 at 3:19?AM Tomas Kalibera <tomas.kalibera at
gmail.com>
wrote:
>
> On 5/28/25 04:15, Pavel Krivitsky via R-devel wrote:
> > Dear All,
> >
> > Perhaps this should go in r-package-devel, but I suspect that this is
> > going to turn into a feature request, and I want to run it by the list
> > before filing it in the Bugzilla.
> >
> > I would like to specify a long string literal without making the line
> > of code too long. In R,
> >
> > "abc
> > def"
> >
> > yields the string "abc\def", and, as far as I can tell,
there is no
> > mechanism for preventing it from inserting a newline into the string.
> >
> > Putting a backslash before the newline, i.e.,
> >
> > "abc\
> > def"
> >
> > eliminates the newline in (that I know of) C/C++, Python, and Julia,
> > but it makes no difference in R.
> >
> > The implicit concatenation of Python and C/C++, e.g., "abc"
"def", is a
> > syntax error as well in R.
> >
> > It is, of course, possible to use paste0(), but is there a more
concise
> > built-in mechanism in R of which I am not aware?
> >
> > If not, I think it would make sense to bring R in line with the
others.
> > Currently, backslash and no backslash before a newline behave
> > identically (at least as far as I can tell), so I doubt that a
> > nontrivial amount of code relies on the current behaviour. [1]
>
> What would be real example of a long string literal you would want to
> enter this way?
>
> For entering a long text with newlines, one can use raw strings in R
> (see ?Quotes) - but there you would see the newlines and indentation.
> I've seen code where  "paste0" has been aliased to a local
function
> named with a single letter to make concatenation more concise.
>
> Best
> Tomas
>
> >
> >                               Any thoughts?
> >                               Pavel
> >
> > [1] On the off chance that it does, it should easy to check by
> > searching for "\\\n" in package sources, because a backslash
before a
> > newline is a syntax error outside a string.
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
	[[alternative HTML version deleted]]

On 6/2/25 17:37, Josiah Parry wrote:
> Tomas,
>
> Here is a good example of where this functionality would be useful:
>
https://github.com/R-ArcGIS/arcgislayers/blob/2b29f4c254e7e5a1dadce8d4b0015a70dfae39d4/R/arc-open.R#L19-L56
>
> In order to prevent R CMD check notes I have to use `paste0()` to 
> concatenate long URLs. If we were able to use `\` to
> separate the string across multiple lines, it would make the solution 
> much nicer!
It may be a matter of taste. To me the current form

#' furl <- paste0(
#'
"https://services3.arcgis.com/ZvidGQkLaDJxRSJ2/arcgis/rest/services/",
#'?? "PLACES_LocalData_for_BetterHealth/FeatureServer/0"
#' )
#'

would be actually clearer than say this:

#' # FeatureLayer
#' furl <- 
"https://services3.arcgis.com/ZvidGQkLaDJxRSJ2/arcgis/rest/services/\
PLACES_LocalData_for_BetterHealth/FeatureServer/0"
#'

Inside a per-line comment (#), a backslash followed by a newline would 
probably be disallowed, anyway - e.g. in C it is considered dangerous 
and is discouraged. And the code resulting from splices is hard to read 
due to missing indentation. There is also risk of accidentally putting a 
space after the backslash before the end of line (which some 
languages/parsers then don't treat as a splice, some do, some issue a 
warning - of course it is hard to see in the code).

The idea of automatically concatenating consecutive string literals as 
in C would not easily work in R. This is now valid R code:

x <- "part1"
"part2"

if we introduced concatenation, we would change behavior of this code 
(the value of x would be different, the result of these two lines would 
be different).

I think paste0() is not that bad in the end.

Best
Tomas
> On Mon, Jun 2, 2025 at 3:19?AM Tomas Kalibera 
> <tomas.kalibera at gmail.com> wrote:
>
>
>     On 5/28/25 04:15, Pavel Krivitsky via R-devel wrote:
>     > Dear All,
>     >
>     > Perhaps this should go in r-package-devel, but I suspect that
>     this is
>     > going to turn into a feature request, and I want to run it by
>     the list
>     > before filing it in the Bugzilla.
>     >
>     > I would like to specify a long string literal without making the
>     line
>     > of code too long. In R,
>     >
>     > "abc
>     > def"
>     >
>     > yields the string "abc\def", and, as far as I can tell,
there is no
>     > mechanism for preventing it from inserting a newline into the
>     string.
>     >
>     > Putting a backslash before the newline, i.e.,
>     >
>     > "abc\
>     > def"
>     >
>     > eliminates the newline in (that I know of) C/C++, Python, and
Julia,
>     > but it makes no difference in R.
>     >
>     > The implicit concatenation of Python and C/C++, e.g.,
"abc"
>     "def", is a
>     > syntax error as well in R.
>     >
>     > It is, of course, possible to use paste0(), but is there a more
>     concise
>     > built-in mechanism in R of which I am not aware?
>     >
>     > If not, I think it would make sense to bring R in line with the
>     others.
>     > Currently, backslash and no backslash before a newline behave
>     > identically (at least as far as I can tell), so I doubt that a
>     > nontrivial amount of code relies on the current behaviour. [1]
>
>     What would be real example of a long string literal you would want to
>     enter this way?
>
>     For entering a long text with newlines, one can use raw strings in R
>     (see ?Quotes) - but there you would see the newlines and indentation.
>     I've seen code where? "paste0" has been aliased to a
local function
>     named with a single letter to make concatenation more concise.
>
>     Best
>     Tomas
>
>     >
>     >? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?Any thoughts?
>     >? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?Pavel
>     >
>     > [1] On the off chance that it does, it should easy to check by
>     > searching for "\\\n" in package sources, because a
backslash
>     before a
>     > newline is a syntax error outside a string.
>     > ______________________________________________
>     > R-devel at r-project.org mailing list
>     > https://stat.ethz.ch/mailman/listinfo/r-devel
>
>     ______________________________________________
>     R-devel at r-project.org mailing list
>     https://stat.ethz.ch/mailman/listinfo/r-devel
>