Now here's an enum *without* associated value types.

Since there are no associated value types the compiler says we can compare instances of this Error type and slaps on the Equatable protocol at compile time.

As it turns out, in Swift, enums with no associated values get free Equatable synthesis!

Here is an enum *with* associated value types:

We could explicitly conform RemoteFeedLoader.Error to Equatable like so, but apparently we don't need to? 🤔

Here's the FeedLoader protocol's implementation class, RemoteFeedLoader.

No where in this code did we explicitly conform the Error type to Equatable:

The puzzle 🧩:

Whenever I commented out the following line in the interface boundary, I would then get the accompanying compile-time error in the test code:

😆 I won’t be passing any Ophthalmology tests, but I enjoyed the UI! Great work!

(6/7)

Now let's see what it would be like to implement the same behavior without this syntax. We could convert this to a do-catch block, like so:

(3/7)

Take a look at the following static function. Why isn't there a do-catch block to catch the potential error that JSONDecoder().decode throws?

💻 Here's the Example Code:

This is the Open／Closed Principle (OCP) in action! We don't have to change the view controller to extend it's behavior.

If we want to add more behavior to the view controller, then we just add another adapter that implements the delegate:

Without it, a view controller's behavior would always be fixed, and Apple's framework wouldn't be very useful 😔

Day 3 of #100DaysOfCode

Log: github.com/webdavis/100...

🧩 Delegates allow us to Extend the Behavior of a Client (1/5)

This is why UIKit.UITableView includes a DataSource／Delegate.

Here's the architecture: