Very simple but handy Publishers extension to create custom AnyPublisher as in RxSwift's Observable<E>.create method

Publishers+Create.swift

// Copy and Paste this in your project
import Combine
import Foundation

extension Publishers {
    struct PublisherObserver<V, E: Swift.Error> {
        private let sendValue: (V) -> Void
        private let sendCompletion: (Subscribers.Completion<E>) -> Void
        
        init(
            _ sendValue: @escaping (V) -> Void,
            _ sendCompletion: @escaping (Subscribers.Completion<E>) -> Void
        ) {
            self.sendValue = sendValue
            self.sendCompletion = sendCompletion
        }
        
        func send(_ value: V) {
            sendValue(value)
        }
        
        func send(completion: Subscribers.Completion<E>) {
            sendCompletion(completion)
        }
    }
    
    static func create<V, E: Swift.Error>(
        observer: (PublisherObserver<V, E>) -> Void
    ) -> AnyPublisher<V, E> {
        let subject = PassthroughSubject<V, E>()
        observer(PublisherObserver(subject.send, subject.send(completion:)))
        return subject.eraseToAnyPublisher()
    }
}

Publishers+CreateExample.swift

import Combine
import Foundation
import PlaygroundSupport

enum AsyncOperationError: Swift.Error {
    case sample
}

func executeAsyncOperationGeneric() -> AnyPublisher<Int, Swift.Error> {
    return Publishers.create { observer in
        DispatchQueue.main.asyncAfter(deadline: .now() + 2.0, execute: {
            observer.send(10)
            observer.send(20)
            observer.send(15)
            observer.send(20)
            observer.send(15)
//            observer.send(completion: .failure(AsyncOperationError.sample))
//            observer.send(completion: .finished)
        })
    }
}

var cancellables = [AnyCancellable]()

executeAsyncOperationGeneric()
    .sink(
        receiveCompletion: { completion in
            switch completion {
            case .failure(let error):
                print("Received error: \(error)")
            case .finished:
                print("Finished successfully")
            }
        },
        receiveValue: { value in
            print("Received value: \(value)")
        }
    )
    .store(in: &cancellables)

PlaygroundPage.current.needsIndefiniteExecution = true

Are you using the Combine framework but missing RxSwift's create method in Observable<E>?
Well, this extension may help you. Just import the first file, Publishers+Create.swift and start using the create method in Publishers as in the example in the second file of this gist.
Take a look at executeAsyncOperationGeneric, it will create an AnyPublisher<Int, Error> using the create method. The example will print:

Received value: 10
Received value: 20
Received value: 15
Received value: 20
Received value: 15