Promises

Promises is a modern framework that provides a synchronization construct for Objective-C and Swift to facilitate writing asynchronous code. Typically, async operations take a completion handler in a form of a block, which is called to provide either a result or an error. To perform more than one async operation, you have to nest the second one inside the completion block of the first one, and also handle an error gracefully. Often such nesting becomes painful to follow or modify. The framework has intuitive APIs that are well documented making it painless to integrate into new or existing code. Supports both Objective-C and Swift. Promises that are created in Objective-C can be used in Swift and vice versa. Has minimum overhead that achieves similar performance to GCD and completion handlers.