Question

R allows for assignment via <- and =.

Whereas there a subtle differences between both assignment operators, there seems to be a broad consensus that <- is the better choice than =, as = is also used as operator mapping values to arguments and thus its use may lead to ambiguous statements. The following exemplifies this:

> system.time(x <- rnorm(10))
   user  system elapsed 
      0       0       0 
> system.time(x = rnorm(10))
Error in system.time(x = rnorm(10)) : unused argument(s) (x = rnorm(10))

In fact, the Google style code disallows using = for assignment (see comments to this answer for a converse view).

I also almost exclusively use <- as assignment operator. However, the almost in the previous sentence is the reason for this question. When = acts as assignment operator in my code it is always accidental and if it leads to problems these are usually hard to spot.

I would like to know if there is a way to turn off assignment via = and let R throw an error any time = is used for assignment.

Optimally this behavior would only occur for code in the Global Environment, as there may well be code in attached namespaces that uses = for assignment and should not break.

(This question was inspired by a discussion with Jonathan Nelson)

Answer 1

Here’s a candidate:

`=` <- function(...) stop("Assignment by = disabled, use <- instead")
# seems to work
a = 1
Error in a = 1 : Assignment by = disabled, use <- instead
# appears not to break named arguments
sum(1:2,na.rm=TRUE)
[1] 3