{{
work on regular objects?The embrace operator {{
should be used exclusively with function arguments:
fn <- function(arg) {
quo(foo({{ arg }}))
}fn(1 + 1)
#> <quosure>
#> expr: ^foo(^1 + 1)
#> env: 0x7ffd89aac518
However you may have noticed that it also works on regular objects:
fn <- function(arg) {
arg <- force(arg)
quo(foo({{ arg }}))
}fn(1 + 1)
#> <quosure>
#> expr: ^foo(^2)
#> env: 0x7ffd8a633398
In that case, {{
captures the value of the expression instead of a defused expression. That's because only function arguments can be defused.
Note that this issue also applies to enquo()
(on which {{
is based).
Ideally we would have made {{
on regular objects an error. However this is not possible because in compiled R code it is not always possible to distinguish a regular variable from a function argument. See Why are strings and other constants enquosed in the empty environment? for more about this.