future (version 0.12.0)

plan: Plan how to resolve a future

Description

This function allows you to plan the future, more specifically, it specifies how future():s are resolved, e.g. by eager or by lazy evaluation.

Usage

plan(strategy = NULL, ..., substitute = TRUE, .call = TRUE)

Arguments

strategy

The evaluation function to use for resolving a future. If NULL, then the current strategy is returned.

substitute

If TRUE, the strategy expression is substitute():d, otherwise not.

.call

(internal) Used to record the call to this function.

...

Additional arguments overriding the default arguments of the evaluation function.

Value

• If a new strategy is chosen, then the previous one is returned (invisible), otherwise the current one is returned (visibly).

Details

The default strategy is eager, which can be set by option future.plan and, if that is not set, system environment variable R_FUTURE_PLAN. To reset the strategy back to the default, use plan("default").

See Also

Evaluation functions provided by this package are eager(), lazy() and multicore(). Other package may provide additional evaluation strategies/functions.

Examples

a <- b <- c <- NA_real_

# A lazy future
plan(lazy)
f <- future({
  a <- 7
  b <- 3
  c <- 2
  a * b * c
})
y <- value(f)
print(y)
str(list(a=a, b=b, c=c)) ## All NAs


# An eager future
plan(eager)
f <- future({
  a <- 7
  b <- 3
  c <- 2
  a * b * c
})
y <- value(f)
print(y)
str(list(a=a, b=b, c=c)) ## All NAs


# A multicore future
plan(multicore)
f <- future({
  a <- 7
  b <- 3
  c <- 2
  a * b * c
})
y <- value(f)
print(y)
str(list(a=a, b=b, c=c)) ## All NAs


## Multisession futures gives an error on R CMD check on
## Windows (but not Linux or OS X) for unknown reasons.
## The same code works in package tests.
# A multisession future
plan(multisession)
f <- future({
  a <- 7
  b <- 3
  c <- 2
  a * b * c
})
y <- value(f)
print(y)
str(list(a=a, b=b, c=c)) ## All NAs