Cocoa Programming for OS X: The Big Nerd Ranch Guide

Making Types Printable

If you use a Vector value in string interpolation, you will not get a very pleasing result:

p​r​i​n​t​l​n​(​"​G​r​a​v​i​t​y​ ​i​s​ ​\​(​g​r​a​v​i​t​y​)​.​"​)​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​"​G​r​a​v​i​t​y​ ​i​s​ ​_​_​l​l​d​b​_​e​x​p​r​_​2​4​7​.​V​e​c​t​o​r​.​"​

You can improve this by conforming to the Printable protocol, which looks like this:

p​r​o​t​o​c​o​l​ ​P​r​i​n​t​a​b​l​e​ ​{​
 ​ ​ ​ ​v​a​r​ ​d​e​s​c​r​i​p​t​i​o​n​:​ ​S​t​r​i​n​g​ ​{​ ​g​e​t​ ​}​
}​

We will cover protocols in more detail in Chapter 6, but the short version is that a protocol defines a set of properties or methods. In order to conform to a protocol, your type must implement the required properties and methods.

To conform to Printable ...