Swift Programming: The Big Nerd Ranch Guide

Closures Are Reference Types

Closures are reference types. This means that when you assign a function to a constant or variable you are actually setting that constant or variable to point to the function. You are not creating a distinct copy of that function. One important consequence of this fact is that any information captured by the function’s scope will be changed if you call the function via a new constant or variable.

To see this, create a new constant and set it equal to your growBy500() function.

Listing 13.13  Duplicate growth

... func makeGrowthTracker(forGrowth growth: Int) -> () -> Int { var totalGrowth = 0 func growthTracker() -> Int { totalGrowth += growth return totalGrowth } return growthTracker } var currentPopulation ...