Generics in Go

As we've mentioned, Go does not support classes. For a long time, that meant that Go code couldn't easily be reused in many circumstances. For example, imagine some code that splits a slice into 2 equal parts. The code that splits the slice doesn't really care about the values stored in the slice. Unfortunately in Go we would need to write it multiple times for each type, which is a very un-DRY thing to do.

func splitIntSlice(s []int) ([]int, []int) {
    mid := len(s)/2
    return s[:mid], s[mid:]
}

func splitStringSlice(s []string) ([]string, []string) {
    mid := len(s)/2
    return s[:mid], s[mid:]
}

In Go 1.20 however, support for generics was released, effectively solving this problem!

Type Parameters

Put simply, generics allow us to use variables to refer to specific types. This is an amazing feature because it allows us to write abstract functions that drastically reduce code duplication.

func splitAnySlice[T any](s []T) ([]T, []T) {
    mid := len(s)/2
    return s[:mid], s[mid:]
}

In the example above, T is the name of the type parameter for the splitAnySlice function, and we've said that it must match the any constraint, which means it can be anything. This makes sense because the body of the function doesn't care about the types of things stored in the slice.

firstInts, secondInts := splitAnySlice([]int{0, 1, 2, 3})
fmt.Println(firstInts, secondInts)

Why Generics?

Generics reduce repetitive code

You should care about generics because they mean you don’t have to write as much code! It can be frustrating to write the same logic over and over again, just because you have some underlying data types that are slightly different.

Generics are used more often in libraries and packages

Generics give Go developers an elegant way to write amazing utility packages. While you will see and use generics in application code, I think it will much more common to see generics used in libraries and packages. Libraries and packages contain importable code intended to be used in many applications, so it makes sense to write them in a more abstract way. Generics are often the way to do just that!

Why did it take so long to get generics?

Go places an emphasis on simplicity. In other words, Go has purposefully left out many features to provide its best feature: being simple and easy to work with.

According to historical data from Go surveys, Go’s lack of generics has always been listed as one of the top three biggest issues with the language. At a certain point, the drawbacks associated with the lack of a feature like generics justify adding complexity to the language.