Checking upfront with guard

We have seen in previous recipes how we can use if statements to check Boolean expressions and unwrap optional values. It's a common use case to want to do some checks and conditional unwrapping at the beginning of a block of code, and then only execute the subsequent code if everything is as expected. This usually results in wrapping the whole block of code in an if statement:

if <#boolean check and unwrapping#> { 
    <#a block of code#> 
    <#that could be quite long#> 
}

Swift has a better solution expressly for this purpose; the guard statement.

In this recipe, we will learn how to use the guard statement to return early from a method.

Getting ready

Let's imagine that we have some data that came from an external source, and we want to turn it into model objects that our code can understand, with the intention of displaying it to the user. We can use guard statements to ensure the data is correctly formatted, bailing early if it...