Performance of Generics in Go: Monomorphization vs Dictionary Passing

Go implements generics via monomorphization, generating type-specific code at compile time to ensure zero runtime overhead compared to dictionary passing.

Go uses monomorphization, not dictionary passing, to implement generics. The compiler generates a separate copy of generic code for each concrete type used, eliminating runtime type dispatch overhead. This approach ensures that generic functions run at the same speed as non-generic equivalents by resolving all types at compile time.

// The compiler generates distinct functions: SortInt and SortString
func Sort[T comparable](s []T) {
    // Logic compiled once per type T
}

Sort([]int{3, 1, 2})   // Calls SortInt (monomorphized)
Sort([]string{"b", "a"}) // Calls SortString (monomorphized)

Go generics work by creating a unique version of your code for every specific data type you use, rather than using a single generic version that checks types while running. Think of it like a factory that builds a custom machine for each product type instead of one universal machine that slows down to handle everything. This means your generic code runs just as fast as if you had written it specifically for that type.