R devel - Jan 2023 - Recycling in arithmetic operations involving zero-length vectors

Dear R-core,

The language definition is very clear:

"As from R 1.4.0, any arithmetic operation involving a zero-length 
vector has a zero-length result."

Thus, `1 + numeric()` returns `numeric(0)`. However, I don't find this 
very intuitive because usually the shorter vector is recycled to the 
length of the longer vector. Would it be possible to throw at least a 
warning for such cases? I don't expect them to be intended by most users.

Best regards,

-- 
Dr. Roland Fu?

Th?nen-Institut f?r Agrarklimaschutz/
Th?nen Institute of Climate-Smart Agriculture

Bundesallee 65
D-38116 Braunschweig, Germany

Tel.: ++49 531 596 2627
Fax:  ++49 531 596 2699
Email: roland.fuss at thuenen.de

Arbeitsgruppe "Emissionsberichterstattung"/
Working group "Emission Inventories"
Email: emissionsinventare at thuenen.de

Das Johann Heinrich von Th?nen-Institut,
Bundesforschungsinstitut f?r L?ndliche R?ume,
Wald und Fischerei ? kurz: Th?nen-Institut ?
besteht aus 15 Fachinstituten, die in den
Bereichen ?konomie, ?kologie und Technologie
forschen und die Politik beraten.

The Johann Heinrich von Th?nen Institute,
Federal Research Institute for Rural Areas,
Forestry and Fisheries ? Th?nen Institute in brief ?
consists of 15 specialized institutes that
carry out research and provide policy advice
in the fields of economy, ecology and technology.

On 16/01/2023 5:23 a.m., Roland Fu? wrote:
> Dear R-core,
> 
> The language definition is very clear:
> 
> "As from R 1.4.0, any arithmetic operation involving a zero-length
> vector has a zero-length result."
> 
> Thus, `1 + numeric()` returns `numeric(0)`. However, I don't find this
> very intuitive because usually the shorter vector is recycled to the
> length of the longer vector. Would it be possible to throw at least a
> warning for such cases? I don't expect them to be intended by most
users.
> 
> Best regards,
The previous paragraph says "If the length of the longer vector is not a 
multiple of the shorter one, a warning is given."  Since 1 is not a 
multiple of 0, that implies a warning should be given here.

However, R 1.4.0 was released more than 20 years ago, so I would guess 
there are lots of packages intentionally using this.  For example, it's 
a way to propagate bad inputs through a long calculation that allows a 
single test at the end.

And even unintentional uses are unlikely to lead to problematic results: 
  numeric(0) is usually a pretty clear signal that something is wrong.

So I'd suggest a documentation change: "As from R 1.4.0, any arithmetic
operation involving a zero-length vector has a zero-length result 
*without a warning*."

Duncan Murdoch