future (version 0.8.0)

eager: Create an eager future whose value will be resolved immediately

Description

An eager future is a future that uses eager evaluation, which means that its value is computed and resolved immediately, which is how regular expressions are evaluated in R. This type of future exists mainly for the purpose of troubleshooting code that fails with other types of futures.

Usage

eager(expr, envir = parent.frame(), substitute = TRUE, local = TRUE, ...)

Arguments

expr

An R expression.

envir

The environment in which the evaluation is done (or inherits from if local is TRUE).

substitute

If TRUE, argument expr is substitute():ed, otherwise not.

local

If TRUE, the expression is evaluated such that all assignments are done to local temporary environment, otherwise the assignments are done in the calling environment.

...

Not used.

Value

• An EagerFuture.

Details

The preferred way to create an eager future is not to call this function directly, but to register it via plan(eager) such that it becomes the default mechanism for all futures. After this future() and %<=%< a=""> will create eager futures.

Examples

## A global variable
a <- 0

## Create eager future (explicitly)
f <- eager({
  b <- 3
  c <- 2
  a * b * c
})

## Since 'a' is a global variable in _eager_ future 'f',
## it already has been resolved, and any changes to 'a'
## at this point will _not_ affect the value of 'f'.
a <- 7
print(a)

v <- value(f)
print(v)
stopifnot(v == 0)