Examination of tidyeval's quosure

uncovering-the-tidyeval-quosure.R

library(rlang)

# Underneath the hood of a quosure ------------------------------------

v <- "a variable"
vquo <- quo(v)

print(vquo)
#> <quosure>
#> expr: ^v
#> env:  global

class(vquo)
#> [1] "quosure" "formula"
typeof(vquo)
#> [1] "language"

unclass(vquo)
#> ~v
#> attr(,".Environment")
#> <environment: R_GlobalEnv>


# Evaluating a quosure ----------------------------------------------------

# Persistent un-evalability (turns eval() into quote())
vquo_env <- attr(vquo, ".Environment")
eval(vquo, envir = vquo_env)
#> <quosure>
#> expr: ^v
#> env:  global

# Symbolic expressions (i.e. ~v) are subsettable
length(vquo)
#> [1] 2
vquo[[1L]]
#> `~`
vquo[[2L]]
#> v
class(vquo[[2L]])
#> [1] "name"

# Take advantage of this to evaluate our symbol/call
eval(vquo[[2L]], envir = vquo_env)
#> [1] "a variable"


# Further exploration -----------------------------------------------------

a <- 5
b <- 6

abquo <- quo(a + b)
abquo_env <- attr(abquo, ".Environment")

evalq(abquo[[2L]], envir = abquo_env)
#> [1] 11
evalq(abquo[[2L]], envir = abquo_env)
#> a + b