Stub Function Arguments

stub() assigns all arguments of a given function as symbols to the specified environment (usually the current environment). For arguments without default values, stub() will attempt to retrieve their values from .GlobalEnv if they exist there.

Usage

stub(func, ..., envir = parent.frame())

Arguments

func

function for which the arguments should be stubbed

...

non-default arguments of func

envir

environment to which symbols should be assigned

Value

list of symbols that are assigned to envir

Details

Stub is thought to be used for interactive testing and unit testing. It does not work for primitive functions.

When a function has required arguments without defaults, stub() will first check if those arguments exist in .GlobalEnv and use their values if found. This enables a common dev workflow: (1) Run example code that sets variables, (2) Call stub(func), (3) Modify and execute parts of the function body.

Examples

f <- function(x, y = 2, z = 3) x + y + z
args <- stub(f, x = 1) # assigns x = 1, y = 2 and z = 3 to current env
#> Created 3 variables in anonymous environment:
#>  $ x: num 1
#>  $ y: num 2
#>  $ z: num 3

# stub() can also use values from GlobalEnv for missing args:
g <- function(a, b = 10) a + b
a <- 5 # Set in GlobalEnv
stub(g) # Uses a = 5 from GlobalEnv, assigns a = 5 and b = 10
#> Error in stub(g): argument 'a' is missing, with no default and not found in .GlobalEnv