Go - Generics

Generic Functions

func Map[T any, R any](in []T, f func(T) R) []R {
  out := make([]R, len(in))
  for i, v := range in { out[i] = f(v) }
  return out
}

Constraints

type Number interface{ ~int | ~int64 | ~float64 }
func Sum[T Number](xs ...T) T {
  var s T
  for _, x := range xs { s += x }
  return s
}

Guidelines

• Use generics when it clarifies code or removes duplication.
• Prefer concrete types when behavior is specific.

Common errors

• Overusing generics—prefer concrete types unless duplication or clarity improves.

Practice

• Write Map[T any, R any] and test it with []int and []string.

Quick quiz

1. What’s a type constraint?