carrier (version 0.1.1)

crate: Crate a function to share with another process

Description

crate() creates functions in a self-contained environment (technically, a child of the base environment). This has two advantages:

• They can easily be executed in another process.

• Their effects are reproducible. You can run them locally with the same results as on a different process.

Creating self-contained functions requires some care, see section below.

Usage

crate(.fn, ...)

Arguments

.fn

A fresh formula or function. "Fresh" here means that they should be declared in the call to crate(). See examples if you need to crate a function that is already defined. Formulas are converted to purrr-like lambda functions using rlang::as_function().

...

Arguments to declare in the environment of .fn. If a name is supplied, the object is assigned to that name. Otherwise the argument is automatically named after itself.

Creating self-contained functions

• They should call package functions with an explicit :: namespace. This includes packages in the default search path with the exception of the base package. For instance var() from the stats package must be called with its namespace prefix: stats::var(x).

• They should declare any data they depend on. You can declare data by supplying additional arguments or by unquoting objects with !!.

Examples

# You can create functions using the ordinary notation:
crate(function(x) stats::var(x))

# Or the formula notation:
crate(~ stats::var(.x))

# Declare data by supplying named arguments. You can test you have
# declared all necessary data by calling your crated function:
na_rm <- TRUE
fn <- crate(~ stats::var(.x, na.rm = na_rm))
try(fn(1:10))

# For small data it is handy to unquote instead. Unquoting inlines
# objects inside the function. This is less verbose if your
# function depends on many small objects:
fn <- crate(~ stats::var(.x, na.rm = !!na_rm))
fn(1:10)

# One downside is that the individual sizes of unquoted objects
# won't be shown in the crate printout:
fn


# The function or formula you pass to crate() should defined inside
# the crate() call, i.e. you can't pass an already defined
# function:
fn <- function(x) toupper(x)
try(crate(fn))

# If you really need to crate an existing function, you can
# explicitly set its environment to the crate environment with the
# set_env() function from rlang:
crate(rlang::set_env(fn))