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With the arrival of combine framework, is there a need to use operation queues anymore. For example, apple uses operation queues almost all over the place in WWDC app. So if we use SwiftUI with combine(asynchronous programming), will there be a need to use Operation Queues?
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The Combine framework provides a declarative Swift API for processing values over time. These values can represent many kinds of asynchronous events. Combine declares publishers to expose values that can change over time, and subscribers to receive those values from the publishers.
GCD tends to be simpler to work with for simple tasks you just need to execute and forget. Operations provide much more functionality when you need to keep track of a job or maintain the ability to cancel it. If you're just working with methods or chunks of code that need to be executed, GCD is a fitting choice.
Here are how operation queues are different from dispatch queues: In operation queues, you can set priority for your operations and also you can add dependencies to the operations which means you can define that some operation execute only after the completion of other operations.
You can safely use a single OperationQueue object from multiple threads without creating additional locks to synchronize access to that object.
Combine is just another asynchronous pattern, but doesn’t supplant operation queues (or dispatch queues). Just as GCD and operation queues happily coexist in our code bases, the same is true with Combine.
GCD is great at easy-to-write, yet still highly performant, code to dispatching tasks to various queues. So if you have something that might risk blocking the main thread, GCD makes it really easy to dispatch that to a background thread, and then dispatch some completion block back to the main thread. It also handles timers on background threads, data synchronization, highly-optimized parallelized code, etc.
Operation queues are great for higher-level tasks (especially those that are, themselves, asynchronous). You can take these pieces of work, wrap them up in discrete objects (for nice separation of responsibilities) and the operation queues manage execution, cancelation, and constrained concurrency, quite elegantly.
Combine shines at writing concise, declarative, composable, asynchronous event handling code. It excels at writing code that outlines how, for example, one’s UI should reflect some event (network task, notification, even UI updates).
This is obviously an oversimplification, but those are a few of the strengths of the various frameworks. And there is definitely overlap in these three frameworks, for sure, but each has its place.
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