Swift Programming: The Big Nerd Ranch Guide

A Quick Note on Type Inference

Take a look at this code that you entered earlier:

for i in 1...5 {
    ++myFirstInt
    print("myFirstInt equals \(myFirstInt) at iteration \(i)")
}

Notice that i is not declared to be of the Int type. It could be, as in: for i: Int in 1...5 (the let portion of the declaration is assumed by the syntax for you). But it is not necessary. The type of i is inferred from its context. In this example, i is inferred to be of type Int because the specified range contains integers.

Type inference is handy. It lets you type less, which makes for fewer typos. However, there are a few cases where you need to specifically declare the type. We will highlight those when they come up. In general, however, we recommend ...