Type constraints

Type constraints in Go are defined using the type keyword with a ~ prefix or a list of interfaces to restrict generic type parameters. They ensure that only types satisfying specific conditions can be used with a generic function or type.

// Define a constraint allowing any type that supports addition
type Addable interface {
  int | int8 | int16 | int32 | int64 | float32 | float64 | ~string
}

// Use the constraint in a generic function
func Sum[T Addable](items ...T) T {
  var total T
  for _, item := range items {
    total += item
  }
  return total
}

Type constraints act like a rulebook for generic code, specifying exactly which data types are allowed to be used. Think of it like a vending machine that only accepts coins of a certain size; if you try to use a bill, it won't work. This prevents errors by ensuring your code only runs with compatible data types.