However, there is no need to chain futures in your use case, because there is only one asynchronous operation, namely the call to requestAccess. If you want to encapsulate the result of an operation that might throw an error, like your fetchContactswhat you want to return is not a Future but a Result. To illustrate, I'll create a possible pipeline that does what you describe. Throughout the discussion, I'll first show some code, then discuss that code, in that order.
In checkAccesswe look to see whether we have authorization. There are only two cases of interest; either we are authorized, in which case we can proceed to access our contacts, or we are not determined, in which case we can ask the user for authorization.
The other possibilities are of no interest: we know we have no authorization and we cannot request it. So I characterize the result, as I said earlier, as a Result:.
So I generate a Future. There are only two possibilities: either we will get an error or we will get a Bool that is true. There are no circumstances under which we get no error but a false Bool. So I either call the promise's failure with the error or I call its success with the Bool, which I happen to know will always be true. Such an operation can throw, so I express it once again as a Result.
Our call to checkAccess yields a Result. But a Result has a publisher! So that publisher is the start of our chain. If the Result didn't get an error, this publisher will emit a Bool value. If it did get an error, the publisher will throw it down the pipeline. This is the only interesting step along the pipeline. We receive a Bool. If it is true, we have no work to do; but if it is false, we need to get our Future and publish it.
The way you publish a publisher is with. But what if gotAccess is true? We still have to return a publisher, and it needs to be of the same type as our Future. It doesn't actually have to be a Future, because we can erase to AnyPublisher.
But it must be of the same typesnamely Bool and Error.In other words, it allows you to write functional reactive code in a declarative way using Swift.
Functional reactive programming FRP is a special paradigm used to deal with asynchronous code. It's a special kind of functional programmingwhere you are working with async streams of values. So basically you can process and transform values over time using functional methods like mapflatMapetc.
Combine is the "native" Swift implementation of this programming paradigm, made by Apple. I already made a brief networking example of using Combinewhich is good if you're just looking for a simple code snippet to simplify your URLSession requests.
Allow me to grab one example and paste it here again, I'll show you why The most important thing here is the new dataTaskPublisher method. It creates Publisher that can send aka. Moving forward to the next few lines we can see examples of various Operator functions mapdecodereplaceErrorereaseToAnyPublisher. They are special functional methods and they always return a Publisher. By using operators you can chain a bunch of publishers together, this gives us that nice declarative syntax that I mentioned before.
Functional programming is awesome! The final member of the Combine family is the Subscriber. Since we can publish all sort of things, we can assume that on the other end of the publisher chain, there will be some sort of object that's going to use our final result. Staying with our current example, the sink method is a built-in function that can connect a publisher to a subscriber.
You'll learn the other one later on I believe that Combine is a huge leap forward and everyone should learn it. My only concern is that you can only use it if you are targeting iOS13 or above, but this will fade away in a blink with time, just like it was with collection and stack views. This is the future of aysnc programming on Apple plaftorms, and it's brighter than it was ever before. Oh, by the way you might ask the question My advice is to stay with your current favorite solution for about one year but only if you are happy with it.
You will see how amazing it is to work with this framework, so I if you are still not convinced, it's time toThey talk to web services, carry out complex computations and pass around high-resolution media files.
These operations must be asynchronous so that the app remains responsive to users. The usual approach to asynchronous programming in Swift is callback-based. However, the following caveats apply  :.
If you are new to Combine, Getting Started with Combine will get you up to speed. Future is a context for a value that might not yet exist. Generally, we use a future to represent the eventual completion or failure of an asynchronous operation. Future has two types that represent the type of value it wraps and the type of error it can fail with.
In our example, these are Int and Never correspondingly. Promise is essentially a closure that accepts a single Result parameter. This is why Future has a callback-based initializer. Future is one-shotmeaning that it finishes immediately after we pass a value or an error to its promise:. Futures and promises provide first-class language support for asynchronous computations. This results in several profound consequences, which are very difficult to achieve with callbacks:. The callback-based approach scales poorly.
With only three requests, we end up having lots of branches and five levels of nesting. The shape of such code is notoriously known as a callback hell.
On the second benefit, we never deal with nil values explicitly. Conversely, in the previous example, we get triple optionals in the callback. Futures eliminate the entire class of errors related to having nil values or nil errors. With callbacks, we would have to resort to higher-level APIs, like Grand Central Dispatch or OperationQueueand it would still be a non-trivial task. However, it is straightforward to achieve with futures:.
Moreover, not only can we put futures in systematic ways, but we can transform their results, without removing them from the future context. Here I highlight commonly used transform operators in Combine. What if a future is rejected? In this case, Combine provides plenty error handling options at our disposal. Debugging futures and promises is different from the traditional methods, like manually setting breakpoints and examining stack traces.
I explain four troubleshooting techniques in Debugging with Swift Combine Framework. We use a future to represent an asynchronous computation and we use a promise to deliver a value or an error to the future.Практическое применение фреймворка Combine в UIKit и SwiftUI
Futures and promises lend themselves to delivering a clean and scalable implementation of a compositional asynchronous programming model. The Swift Combine framework provides native implementation of futures and promises along with a rich set of operations. For all these reasons, I endorse futures and promises as the direction of the asynchronous programming in Swift. If you enjoyed this post, be sure to follow me on Twitter to not miss any new content.
However, the following caveats apply  : Async programming with callbacks is hard to manage. It violates the inversion of control.
Futures and promises have none of these drawbacks. Why futures and promises are the direction of the asynchronous programming in Swift? How to use futures and promises with the Swift Combine framework? How to migrate from callbacks to futures? Understanding Futures and Promises Future is a context for a value that might not yet exist.Publishes a single Boolean value that indicates whether all received elements pass a given predicate.
Raises a fatal error when its upstream publisher fails, and otherwise republishes all received input. Collects all received elements, and emits a single array of the collection when the upstream publisher finishes. Collects up to the specified number of elements, and then emits a single array of the collection. Subscribes to an additional publisher and publishes a tuple upon receiving output from either publisher.
Subscribes to two additional publishers and publishes a tuple upon receiving output from any of the publishers. Subscribes to an additional publisher and invokes a closure upon receiving output from either publisher. Subscribes to three additional publishers and publishes a tuple upon receiving output from any of the publishers. Subscribes to two additional publishers and invokes a closure upon receiving output from any of the publishers.
Subscribes to three additional publishers and invokes a closure upon receiving output from any of the publishers. Delays delivery of all output to the downstream receiver by a specified amount of time on a particular scheduler. Ignores elements from the upstream publisher until it receives an element from a second publisher. Omits elements from the upstream publisher until a given closure returns false, before republishing all remaining elements.
Publishes only the last element of a stream that satisfies a predicate closure, after the stream finishes. Publishes the maximum value received from the upstream publisher, using the provided ordering closure.
Combines elements from this publisher with those from another publisher of the same type, delivering an interleaved sequence of elements. Combines elements from this publisher with those from two other publishers, delivering an interleaved sequence of elements.
Combines elements from this publisher with those from three other publishers, delivering an interleaved sequence of elements.
Asynchronous Programming with Futures and Promises in Swift with Combine Framework
Combines elements from this publisher with those from four other publishers, delivering an interleaved sequence of elements. Combines elements from this publisher with those from five other publishers, delivering an interleaved sequence of elements. Combines elements from this publisher with those from six other publishers, delivering an interleaved sequence of elements. Combines elements from this publisher with those from seven other publishers, delivering an interleaved sequence of elements.
Applies a closure that accumulates each element of a stream and publishes a final result upon completion. Attempts to recreate a failed subscription with the upstream publisher using a specified number of attempts to establish the connection.
Transforms elements from the upstream publisher by providing the current element to a closure along with the last value returned by the closure.
Flattens the stream of events from multiple upstream publishers to appear as if they were coming from a single stream of events. Publishes either the most-recent or first element published by the upstream publisher in the specified time interval. Terminates publishing if the upstream publisher exceeds the specified time interval without producing an element. Publishes a single Boolean value that indicates whether all received elements pass a given error-throwing predicate.
Cannot convert return expression of type 'Publishers. I tried using flatMap but with a similar error.
I suppose I can wrap the body of getImage in a future but that doesn't seem as clean as chaining and mapping. Any suggestions would be welcome. You can't use dribs and drabs and bits and pieces from the Combine framework like that.
You have to make a pipeline — a publisher, some operators, and a subscriber which you store so that the pipeline will have a chance to run.
The ultimate Combine framework tutorial in Swift
So, here, getItem is a function that produces your Publisher, a Future. So you can say. Now the future and the whole pipeline will run asynchronously and the result will pop out the end of the pipeline and you can do something with it. Now, of course you can put the Future and the Map together and then stop, vending them so someone else can attach other operators and a subscriber to them. You have now assembled the start of a pipeline and no more. And there's nothing wrong with that! Learn more.
Asked 1 month ago. Active 1 month ago. Viewed 58 times. Kon Kon 3, 3 3 gold badges 14 14 silver badges 29 29 bronze badges. Active Oldest Votes. So you can say getItem In my case, getItem is a private function, and I'd like to expose getImage to the user, who will then create the subscription. I'd like to create the pipeline up to the point of sink as part of getImage and expose a simple Future to the user. With a publisher, I can do that and eraseToAnyPublisher to hide the details.College Stats.
His last name is fitting. His footwork stands out above all the traits at his disposal. He can plant, jump cut and then he is off to the races. Swift has often showcased his spin move at maximum acceleration without losing any momentum in the open field.
Something that will treat him well at the next level. Balance, balance, balance. Swift shows good balance when running with the ball with a low center of gravity. It can prove difficult to knock him to the turf with just a shoulder or arm tackles.
Defenses will have to find a way to square the back and wrap him up when attempting to bring him down. In the NFL a running back has to be involved in the passing game to avoid any tells as to what the offense is looking to do. He is just as much a weapon in that aspect of the game. If a defense losing track of the back, he will make you pay once he gets the ball in his hands.
As with any running back in the class, Swift will need to focus on his pass protecting technique at the NFL level. To be a feature back and a three-down option, protecting his quarterback must be a priority for Swift to make an impact at the next level. He has the tools available so his development in this area should come early on in his NFL career.
Durability is going to be a concern, not just on the injury front. At Georgia he never had more than touches on offense, so a heavier workload will be a concern moving forward. He did play in 43 games over three seasons but he will need ways to protect his body at one of the most violent positions on the offensive side of the ball. Not to mention that Swift does have a punishing run style at times. Swift is likely the top rated running back on most draft boards and could be the first one selected in the NFL Draft.
Despite the position being devalued over the years, there is a lot of value in taking a back the caliber of Swift with four to five years of control at a lower cost. It's time to put the finishing touches on our interior offensive line rankings for the NFL Draft! Every NFL draft prospect travels their own unique journey to get to the pro ranks, and Utah safety Terrell Burgess is no exception. Though it took a while for him to get his opportunity as a full-time starter, Burgess made the most of it last season, establishing himself as one of the best players in the country at his position.
Burgess recently spoke exclusively with Draft Wire about his football journey, his experience at the NFL Scouting Combine, and what kind of player he'll be at the next level. JM: You spent some time playing both wide receiver and defensive back during When looking for a cornerback who can play on the boundary in the NFL, teams like players with confidence who aren't afraid to engage in physical contact. Temple's Harrison Hand is a prospect who fits that bill.
Coming off of a season in which he tallied a team-leading three interceptions and five pass deflections, he is looking to carry on his success as he prepares to play at the next level. Draft Wire recently spoke exclusively with Hand about his competitive mindset, his preparations for the draft, his NFL bloodline, and what he brings to the table as a potential draft Please enter an email address.Last week, I released some machine learning model results that attempted to predict WR success.
Evaluating an RB prospect before the NFL draft requires careful examination as draft capital is a huge part…. While Fant owns an average draft position ADP of The Texans also do not have a first-round pick and actually do not select all the way until the 57th pick. In eight game with the Cardinals last year, Drake averaged Even if Gurley was at his worst last season, averaging 3. Reportedly, the Los Angeles Chargers were also interested in Brady but were not able to get his signature.
Per NFL. That sort of positional mystique definitely plays into the hype train behind Swift who many have ranked as the best fantasy football prospect in this years draft class. The 17 receptions as a true freshman are a positive indicator.
The 81 rushing attempts mostly came in blowouts but it is worth noting he had 88 yards and a touchdown against Auburn and 94 yards on only six carries against Mizzou as a true freshman. To me, this has to be considered a negative. Holyfield and Swift both averaged exactly 6. In his final season at Georgia, Swift racked up carries for 1, yards while ceding carries to Brian Herrien and 78 to Zamir White.
In his college career, Swift topped 20 carries in a game only three times though he had seven games with four or more receptions. He also dipped down to only 24 receptions. In making a purely statistical case for Swift, you have a few issues. It is a little controversial to assume that Jonathan Taylor is a better player than Swift or that Taylor will be drafted before Swift but that is the official RotoExperts stance as of right now.
The allure of a high-pedigree back without much wear and tear who will be drafted highly and immediately expected to catch passes is a pretty awesome combination. Along with adequate long speed, he is much more agile than you would expect from a player of his size. His quick feet match his quick decision making. Is always searching for space, and has good vision for it — in clutter and the open field. Is a down-and-distance versatile runner who has the potential to be a very reliable three down back in the NFL.
The controversial stance of ranking Jonathan Taylor and maybe even J. There is a decent chance that Swift is used like a fancy version of Jalen Richard, at least the beginning of his career. While Swift probably has more Kamara-like upside than most running backs in the draft class, his floor due to a lack of true workhorse-level workload means that he is probably not the correct answer at the 1.
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