The goal of factory is to make construction of function factories more straightforward, without requiring the user to learn the rlang package.

Installation

You can install factory from GitHub with:

# install.packages("remotes")
remotes::install_github("jonthegeek/factory")

Motivation

Function factories are functions that make functions. They can be confusing to work with. For example, they can produce functions that are fragile (examples from Advanced R by Hadley Wickham (2nd Edition), 10.2.3: Forcing Evaluation, “Gah” comments are me):

power1 <- function(exponent) {
  function(x) {
    x ^ exponent
  }
}
x <- 2
square1 <- power1(x)
x <- 3
square1(2) # Gah, fragile!
#> [1] 8

You can make factories that are less fragile, if you remember to force the variables.

power2 <- function(exponent) {
  force(exponent) # Gah, easy to forget!
  function(x) {
    x ^ exponent
  }
}
x <- 2
square2 <- power2(x)
x <- 3
square2(2)
#> [1] 4

However, the resulting function can be hard to understand:

square2
#> function(x) {
#>     x ^ exponent
#>   }
#> <environment: 0x00000000163e5650>

You can make functions that are easier to understand, but building the function factory is much more difficulty (from Advanced R by Hadley Wickham (2nd Edition), 19.7.4: Creating functions):

power3 <- function(exponent) {
  rlang::new_function(
    rlang::exprs(x = ),
    rlang::expr({
      x ^ !!exponent
    }),
    rlang::caller_env()
  )
}

The resulting functions look like a “normal” function, though, and are thus easier for users to understand:

square3 <- power3(2)
square3
#> function (x) 
#> {
#>     x^2
#> }

The goal of factory is to make function factories as straightforward to create as in power1, but to make the resulting functions make as much sense as in power3:

library(factory)
power4 <- build_factory(
  fun = function(x) {
    x ^ exponent
  },
  exponent
)
x <- 2
square4 <- power4(x)
x <- 3
square4(2)
#> [1] 4

The resulting function is clear, as with power3:

square4
#> function (x) 
#> {
#>     x^2
#> }