Because we don’t just want static strings, we want to show the user some sort of relevant data they can use. So, Swift gives us string interpolation as a way of injecting custom data into strings at runtime: it replaces one or more parts of a string with data provided by us.
For example:
var city = “Cardiff”
var message = “Welcome to \(city)!”
Of course, in that trivial example we could have just written our city name directly into the string — “Welcome to Cardiff!” — but in real apps having this inserted dynamically is important because it lets us show real-world user data rather than things we typed ourselves.
Swift is capable of placing any kind of data inside string interpolation. The result might not always be useful, but for all of Swift’s basic types — strings, integers, Booleans, etc — the results are great.
