Declarative-operation.md

Declarative Programming with AOperation

one of the AOperation features is that it supports declarative syntax. Means that you can do all of an operation configs in a chain, without needs of repeatedly refer to the declared property of it. Let see some example. The old way of defining an operation is as below:

let operation = LikeACommentOperation(comment)
operation.addCondition(UserAccessCondition())
operation.didFinish { result in
	// Update UI
}

queue.addOperation(operation)

As you see using AOperation in this way is very tedios and time consuming. But with the new declrative syntax you have this:

LikeACommentOperation(comment)
.conditions(UserAccessCondition())
.didFinish { result in
	// Update UI
}
.add(to: queue)

Very beautiful and neat!

The story does not end here. Using ReceiverOperation protocol you can connect operations to each other like a chain. Each operation receives the result of its back operation:

URLSessionTaskOperation.data(for: url)
.delvier(to: JsonDecoderOperation<[Comments]>)
.didFinish { result in
	// Update UI
}
.add(to: queue)

You can add observers and dependencies this way too:

URLSessionTaskOperation.data(for: url)
.observers(TimeoutObserver(5))
.delvier(to: JsonDecoderOperation<[Comments]>)
.didFinish { result in
    // Update UI
}
.add(to: queue)

Using RetryableOperation protocol you can handle failure situations and retry the chain as number as you need:

URLSessionTaskOperation.data(for: url)
.delvier(to: JsonDecoderOperation<[Comments]>)
.retryOnFailure { (numberOfRetries, error, retry) in
	retry(numberOfRetries < 1)
}
.didFinish { result in
    // Update UI
}
.add(to: queue)

Note that you should always use add(to:) mehtod at the end of the chain.

The new declarative syntax of AOperation makes using it easy and enjoyable.