Combine multiple promise objects — promise

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)

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 ....

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.

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)
  })