Struct promises::Promise
[−]
[src]
pub struct Promise<T: Send, E: Send> { // some fields omitted }
A promise is a way of doing work in the background. The promises in this library have the same featureset as those in Ecmascript 5.
Promises
Promises (sometimes known as "futures") are objects that represent
asynchronous tasks being run in the background, or results which
will exist in the future.
A promise will be in state of running, fulfilled, or done. In order to
use the results of a fulfilled promise, one attaches another promise
to it (i.e. via then
). Like their Javascript counterparts, promises can
return an error (of type E
).
Panics
If the function being executed by a promise panics, it does so silently.
The panic will not resurface in the thread which created the promise,
and promises waiting on its result will never be called. In addition,
the all
and race
proimse methods will ignore "dead" promises. They
will remove promises from their lists, and if there aren't any left
they will silently exit without doing anything.
Unfortunately, panics must be ignored for two reasons:
* Panic messages don't have a concrete type yet in Rust. If they did,
promiess would be able to inspect their predecessors' errors.
* Although a Receiver
can correctly handle its paired Sender
being
dropped, such as during a panic, for reasons stated above the "message"
of the panic is not relayed.
Finally, Ecmascript promises themselves do have the ability to return
and error type, represented as a Result<T, E>
here. Thus, one should
use try!
and other error handling rather than calls to unwrap()
.
Methods
impl<T: Send + 'static, E: Send + 'static> Promise<T, E>
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fn then<T2, E2>(self, callback: fn(t: T) -> Result<T2, E2>, errback: fn(e: E) -> Result<T2, E2>) -> Promise<T2, E2> where T2: Send + 'static, E2: Send + 'static
Chains a function to be called after this promise resolves.
fn then_result<T2, E2>(self, callback: fn(r: Result<T, E>) -> Result<T2, E2>) -> Promise<T2, E2> where T2: Send + 'static, E2: Send + 'static
Chains a function to be called after this promise resolves,
using a Result
type.
fn new<F>(func: fn() -> Result<T, E>) -> Promise<T, E>
Creates a new promsie, which will eventually resolve to one of the
values of the Result<T, E>
type.
fn race(promises: Vec<Promise<T, E>>) -> Promise<T, E>
Applies a promise to the first of some promises to become fulfilled.
fn all(promises: Vec<Promise<T, E>>) -> Promise<Vec<T>, E>
Calls a function with the result of all of the promises, or the error of the first promise to error.
fn resolve(val: T) -> Promise<T, E>
Creates a promise that resolves to a value
fn reject(val: E) -> Promise<T, E>
Creates a promise that resolves to an error.
fn from_result(result: Result<T, E>) -> Promise<T, E>
Creates a new promise that will resolve to the result value.