collector

draft for discussion

Installation

Install with

pak::pak("cynkra/collector")

Examples

collector() creates a new function, with an altered body but the same environment:

library(collector)
add <- function(x, y) {
  x + y
}
environment(add) <- asNamespace("stats")
add2 <- collector(add)
add2
#> function(x, y) {
#>   globals[["add"]]$args <- constructive::construct_reprex()
#>   globals[["add"]]$call <- constructive::deparse_call(sys.call())
#>   on.exit(globals[["add"]]$return_value <- returnValue())
#>   {
#>     x + y
#>   }
#> }
#> <environment: namespace:stats>

It behaves the same as the original but additionally it collects :

• The arguments
• The call
• The return value

a <- 1
b <- 2
add2(a, b)
#> [1] 3

collected("add")
#> $args
#> delayedAssign("x", value = a, eval.env = .GlobalEnv)
#> delayedAssign("y", value = b, eval.env = .GlobalEnv)
#> 
#> $call
#> add2(a, b)
#> 
#> $return_value
#> [1] 3

Note the use of delayedAssign() because arguments are not evaluated yet at the start of the body, this is robust to functions that use NSE.

If we know we don’t use NSE, we can use force = TRUE

# if we 
add3 <- collector(add, force = TRUE, name = "custom_name")
add3(a, b)
#> [1] 3
collected("custom_name")
#> $args
#> x <- 1
#> 
#> y <- 2
#> 
#> 
#> $call
#> add3(a, b)
#> 
#> $return_value
#> [1] 3

Or we can choose

# if we 
add4 <- collector(add, force = "x", name = "custom_name2")
add4(a, b)
#> [1] 3
collected("custom_name2")
#> $args
#> x <- 1
#> 
#> delayedAssign("y", value = b, eval.env = .GlobalEnv)
#> 
#> $call
#> add4(a, b)
#> 
#> $return_value
#> [1] 3