Sample code for a UIPageViewController implementation. Two versions, one with wraparound between first and last page, and one without.

MyPageViewController-NoWrap.swift

//
//  MyPageViewController.swift
//  PageViewExperiment
//
//  Adapted from http://samwize.com/2015/10/13/how-to-create-uipageviewcontroller-in-storyboard-in-container-view/
//  Updated for Swift 3 and (IMHO) minor code style improvements, and modified page turning behavior to not wrap around
//

import UIKit

class MyPageViewController: UIPageViewController {
	var pages = [UIViewController]()

	override func viewDidLoad() {
		super.viewDidLoad()

		dataSource = self

		let page1: UIViewController! = storyboard?.instantiateViewController(withIdentifier: "page1")
		let page2: UIViewController! = storyboard?.instantiateViewController(withIdentifier: "page2")

		pages.append(page1)
		pages.append(page2)

		setViewControllers([page1], direction: .forward, animated: false, completion: nil)
	}
}

extension MyPageViewController: UIPageViewControllerDataSource {
	func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {

		let currentIndex = pages.index(of: viewController)!

		// This version will not allow pages to wrap around
		guard currentIndex > 0 else {
			return nil
		}

		return pages[currentIndex - 1]
	}

	func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {

		let currentIndex = pages.index(of: viewController)!

		// This version will not allow pages to wrap around
		guard currentIndex < pages.count - 1 else {
			return nil
		}

		return pages[currentIndex + 1]
	}

	func presentationCount(for pageViewController: UIPageViewController) -> Int {
		return 2
	}

	func presentationIndex(for pageViewController: UIPageViewController) -> Int {
		return 0
	}
}

MyPageViewController-Wrap.swift

//
//  MyPageViewController.swift
//  PageViewExperiment
//
//  Adapted from http://samwize.com/2015/10/13/how-to-create-uipageviewcontroller-in-storyboard-in-container-view/
//  Updated for Swift 3 and (IMHO) minor code style improvements
//

import UIKit

class MyPageViewController: UIPageViewController {
	var pages = [UIViewController]()

	override func viewDidLoad() {
		super.viewDidLoad()

		dataSource = self

		let page1: UIViewController! = storyboard?.instantiateViewController(withIdentifier: "page1")
		let page2: UIViewController! = storyboard?.instantiateViewController(withIdentifier: "page2")

		pages.append(page1)
		pages.append(page2)

		setViewControllers([page1], direction: .forward, animated: false, completion: nil)
	}
}

extension MyPageViewController: UIPageViewControllerDataSource {
	func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {

		let currentIndex = pages.index(of: viewController)!
		
		// This math will make the pages wrap around
		let previousIndex = abs((currentIndex - 1) % pages.count)
		return pages[previousIndex]
	}

	func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {

		let currentIndex = pages.index(of: viewController)!
		
		// This math will make the pages wrap around
		let nextIndex = abs((currentIndex + 1) % pages.count)
		return pages[nextIndex]
	}

	func presentationCount(for pageViewController: UIPageViewController) -> Int {
		return 2
	}

	func presentationIndex(for pageViewController: UIPageViewController) -> Int {
		return 0
	}
}

This doesn't work reliably for me:

// This math will make the pages wrap around
let previousIndex = abs((currentIndex - 1) % pages.count)
return pages[previousIndex]

I have 4 pages.
When I start on page 1 and immediately scroll back, it goes to page 2.
When I start on page 1 and scroll forward through page 4, it wraps to page 1, then I can scroll back to page 4.
When I start on page 1 and scroll forward through page 4, it wraps to page 1, then scroll to page 2 and then go backwards it loops back to page 2 instead of page 4.