Type Constraints

A constraint limits which types a generic function can accept.

type_constraints.go

package main

import "fmt"

// Generic shape: Twice[T ~int | ~float64](value T) T
func TwiceInt(value int) int {
	return value + value
}

func main() {
	var count = 
	doubled := TwiceInt(count)

	fmt.Println("count=", count)
	fmt.Println("doubled=", doubled)
	fmt.Println("type=", fmt.Sprintf("%T", doubled))
}

package main

import "fmt"

// Generic shape: Twice[T ~int | ~float64](value T) T
func TwiceInt(value int) int {
	return value + value
}

func main() {
	var count = 
	doubled := TwiceInt(count)

	fmt.Println("count=", count)
	fmt.Println("doubled=", doubled)
	fmt.Println("type=", fmt.Sprintf("%T", doubled))
}

package main

import "fmt"

// Generic shape: Twice[T ~int | ~float64](value T) T
func TwiceInt(value int) int {
	return value + value
}

func main() {
	var count = 
	doubled := TwiceInt(count)

	fmt.Println("count=", count)
	fmt.Println("doubled=", doubled)
	fmt.Println("type=", fmt.Sprintf("%T", doubled))
}

constraint A constraint describes the operations that are valid for a type parameter. The trace uses a concrete integer helper and shows the constrained generic shape in a comment.