How do generics work in Go

Go generics work by defining type parameters in square brackets after a function or type name, allowing the compiler to generate specialized code for each concrete type used. The compiler substitutes the actual types at compile time, ensuring type safety without runtime overhead.

func ToInt[P interface{ ~int }](p P) int { return int(p) }

var IntID = ToInt[int](42)

In this example, P is a type parameter constrained to types underlying int. When ToInt[int] is called, the compiler generates a specific version of the function for int.

Generics let you write functions and types that work with any data type, not just one specific type. Think of it like a reusable mold that can shape different materials into the same form. You use them when you want to avoid copying code for every type you handle, like lists or maps that store different kinds of items.