Bidirectional assignment operator in R

One can define something like:

`%<->%` <- function(x,y){
    t <- y
    assign(deparse(substitute(y)), x, envir=parent.frame())
    assign(deparse(substitute(x)), t, envir=parent.frame()) 
}
a <- 1
b <- 2
a %<->% b
a
[1] 2
b
[1] 1

Such an operator would not make sense with the way R functions:

From Hadley Wickham's book Advanced R, section "Binding basics":

Consider this code:

x <- c(1, 2, 3)

[...] this code is doing two things:

• It’s creating an object, a vector of values, c(1, 2, 3).
• And it’s binding that object to a name, x.

So, for instance, when you run:

a <- 1

you are creating a numerical vector with one element and you are binding it to the name a.

a <-> b

would be binding names to one another, which makes no sense in R.

Also note than when you do:

a <- 1
b <- a
b
# [1] 1

You get 1 as the output, not a, because you create another binding (b) to the numerical vector with the value 1. And when you run b, the output is the object binding to it (1), not another name this object is binding to.

Note: Hadley explains all this very clearly with diagrams in his book.