A generic is very similar to a type alias. The difference is that the exact type of a generic is determined by the context in which it is being used, instead of being determined by the implementing types. This also means that a generic only has a single implementation that must support all possible types. Let's start by defining a generic function.
In Chapter 5, A Modern Paradigm – Closures and Functional Programming, we created a function that helped us find the first number in an array of numbers that passes a test:
func firstInNumbers(
numbers: [Int],
passingTest: (number: Int) -> Bool
) -> Int?
{
for number in numbers {
if passingTest(number: number) {
return number
}
}
return nil
}This would be great if we only ever dealt with arrays of integers, but clearly it would be helpful to be able to do this with other types. In fact, dare I say, all types? We achieve this very simply by making our function generic...