Async library inspired by CommonJS Promises/A spec

http://wiki.commonjs.org/wiki/Promises/A

Installation

Via Cocoapods:

pod 'KSDeferred'

Examples

Creating a deferred object and returning its promise

KSDeferred *deferred = [KSDeferred defer];
return deferred.promise;

Adding callback to the promise

[promise then:^id(id value) {
    .. do something ..
    return value;
  } error:^id(NSError *e) {
    .. handle error ..
    return e;
}];

Chaining promises

KSPromise *chained = [promise then:^id(id value) {
    return value;
} error:^id(NSError *e) {
    return e;
}];

[chained then:^id(id value) {
    # value is value returned from first promise
} error:^id(NSError *e) {
    # error is error returned from first promise
}];

Returning a promise from a callback to chain async work

KSPromise *chained = [promise then:^id(id value) {
    KSDeferred *nextDeferred = [KSDeferred defer];
    return nextDeferred.promise;
} error:^id(NSError *e) {
    return e;
}];

[chained then:^id(id value) {
    # value is value the returned promise resolves with
} error:^id(NSError *e) {
    # error is error the returned promise rejects with
}];

Returning a promise that completes after an array of other promises have completed

KSDeferred *waitForMe1 = [KSDeferred deferred];
KSDeferred *waitForMe2 = [KSDeferred deferred];

KSPromise *joinedPromise = [KSPromise when: @[
    [waitForMe1 promise],
    [waitForMe2 promise]
]];

Resolving a promise

[deferred resolveWithValue:@"VALUE"];

Rejecting a promise

NSError *someError;
[deferred rejectWithError:someError];

Working with generics for improved type safety (Xcode 7 and higher)

KSDeferred<NSDate *> *deferred = [KSDeferred defer];
KSPromise<NSDate *> *promise = deferred.promise;

[deferred resolveWithValue:[NSDate date]];

[promise then:^id(NSDate *date) {
    .. do something ..
    return date;
} error:^id(NSError *e) {
    .. handle error ..
    return e;
}];

Author

• Kurtis Seebaldt, Pivotal Labs

Copyright (c) 2013 Kurtis Seebaldt. This software is licensed under the MIT License.