promises (version 1.4.0)

promise_all: Combine multiple promise objects

Description

Use promise_all to wait for multiple promise objects to all be successfully fulfilled. Use promise_race to wait for the first of multiple promise objects to be either fulfilled or rejected.

Usage

promise_all(..., .list = NULL)
promise_race(..., .list = NULL)

Value

A promise.

For promise_all, if all of the promises were successful, the returned promise will resolve to a list of the promises' values; if any promise fails, the first error to be encountered will be used to reject the returned promise.

For promise_race, the first of the promises to either fulfill or reject will be passed through to the returned promise.

Arguments

...

Promise objects. Either all arguments must be named, or all arguments must be unnamed. If .list is provided, then these arguments are ignored.

.list

A list of promise objects--an alternative to ....

Examples

p1 <- promise(\(resolve, reject) later::later(\() resolve(1), delay = 1))
p2 <- promise(\(resolve, reject) later::later(\() resolve(2), delay = 2))

# Resolves after 1 second, to the value: 1
promise_race(p1, p2) |>
  then(\(x) {
    cat("promise_race:\n")
    str(x)
  })

# Resolves after 2 seconds, to the value: list(1, 2)
promise_all(p1, p2) |>
  then(\(x) {
    cat("promise_all:\n")
    str(x)
  })