Type Parameters and Constraints

func SumCents(values []int64) int64 {
	var total int64
	for _, v := range values {
		total += v
	}
	return total
}

func SumKilograms(values []float64) float64 {
	var total float64
	for _, v := range values {
		total += v
	}
	return total
}
Copy

An order service needs the first function for prices and the second for shipping weights. The two bodies are identical, and only the type names differ. Before Go 1.18, a program had to keep both copies, accept interface{} and lose compile-time checking, or generate the copies with a tool.

Go 1