In RxSwift, we should be careful while passing functions to operators which might cause a memory leak.
In this example, our main actor is RxSwiftTest class. It creates an observable in init and passes multiplyByTwo function to map operator to transform the result. Passing the function causes observable to keep a strong reference to RxSwiftTest instance and RxSwiftTest can not get deallocated and subscription keeps living and printing the result:
Let’s say we have 2 business logics and one needs the other ones’ output to process. Here in this case we can get help from Future in Combine:
The business logic functions returns Future, we tie them up with flatMap and then subscribe with sink function. See that we erased the Future type to AnyPublisher using eraseToAnyPublisher to make it more flexible.
Now, the business logics might return error, in that case we can handle it in many ways with combine. One way of handling would be:
Here, failingBusinessLogic function returns failure and when we subscribe to it, we get completion with error.
One difference between them is CurrentValueSubject has an initial value and emits the latest value to new subscribers. I will show with an example. First, the PassthroughSubject:
As you see, subscription2 does not get any value since PassthroughSubject does not emit latest value. Now, the CurrentValueSubject:
See that, we have to initialize CurrentValueSubject with a value and subscription1 receives this initial value which was the latest by the time subscription1 was initialized. Also, subscription2 receives the latest value when initialized unlike the one in PassthroughSubject example.
Another difference is that you can get the current value of CurrentValueSubject by using its value property:
Also, you can set the value of CurrentValueSubject by using its value property again. (This is equivalent to send function which can be used for both CurrentValueSubject and PassthroughSubject to set the value)
In SwiftUI, shapes are built using paths. To create a custom shape we need to conform to Shape protocol and do the drawing inside path(in:) function. The parameter function takes is a rectangle and it is the reference to the frame that the shape is going to reside. Let’s draw a Cross: