A new Swift video series exploring functional programming and more.
#37 • Monday Nov 12, 2018 • Subscriber-only

Protocol-Oriented Library Design: Part 1

Perhaps the most popular approach to code reuse and extensibility in Swift is to liberally adopt protocol-oriented programming, and many Swift libraries are designed with protocol-heavy APIs. In today’s episode we refactor a sample library to use protocols and examine the pros and cons of this approach.

#37 • Monday Nov 12, 2018 • Subscriber-only

Protocol-Oriented Library Design: Part 1

Perhaps the most popular approach to code reuse and extensibility in Swift is to liberally adopt protocol-oriented programming, and many Swift libraries are designed with protocol-heavy APIs. In today’s episode we refactor a sample library to use protocols and examine the pros and cons of this approach.


Subscribe to Point‑Free

This episode is for subscribers only. To access it, and all past and future episodes, become a subscriber today!

See subscription optionsorLog in

Sign up for our weekly newsletter to be notified of new episodes, and unlock access to any subscriber-only episode of your choosing!

Sign up for free episode


Exercises

  1. There’s one protocol requirement we missed: the fact that we hard-code the path extension of the snapshot reference to “png”. Move this requirement into our protocols. Which protocol does it belong to?

  2. Add a default implementation of path extension so that those conforming their own types to be Snapshottable do not need to declare "png" every time.

  3. Showing the difference between two images is a matter of using a Core Image difference filter. Unfortunately, Apple provides no such API to show the difference between two strings. Implement a line diff algorithm to describe the difference between two strings in Swift.

    A popular, human-readable algorithm is called the “patience diff”. Here are some resources:


References

  • Protocol-Oriented Programming in Swift

    Apple • Tuesday Jun 16, 2015

    Apple’s eponymous WWDC talk on protocol-oriented programming:

    At the heart of Swift’s design are two incredibly powerful ideas: protocol-oriented programming and first class value semantics. Each of these concepts benefit predictability, performance, and productivity, but together they can change the way we think about programming. Find out how you can apply these ideas to improve the code you write.

  • uber/ios-snapshot-test-case

    Uber, previously Facebook

    Facebook released a snapshot testing framework known as FBSnapshotTestCase back in 2013, and many in the iOS community adopted it. The library gives you an API to assert snapshots of UIView’s that will take a screenshot of your UI and compare it against a reference image in your repo. If a single pixel is off it will fail the test. Since then Facebook has stopped maintaining it and transfered ownership to Uber.

  • Snapshot Testing in Swift

    Stephen Celis • Friday Sep 1, 2017

    Stephen gave an overview of snapshot testing, its benefits, and how one may snapshot Swift data types, walking through a minimal implementation.

Chapters
Introduction
00:05
An overview of the problem
01:42
Generalizing screen shot tests
07:08
Generalizing the snapshot format
10:45
Till next time…
22:22
Credits

Hosted by Brandon Williams and Stephen Celis. Recorded in Brooklyn, NY.