The Gotip Playground

package main

import (
	"fmt"
)

// HasID is a structural constraint satisfied by structs with a single field
// called "ID" of type "string".
type HasID interface {
	~struct {
		ID string
	}
}

// CanGetID is an interface constraint satisfied by a type that has a function
// with the signature "GetID() string".
type CanGetID interface {
	GetID() string
}

// Unique satisfies the structural constraint "HasID" *and* the interface
// constraint "CanGetID."
type Unique struct {
	ID string
}

func (u Unique) GetID() string {
	return u.ID
}

// UniqueName does *not* satisfiy the structural constraint "HasID," because
// while UniqueName has the field "ID string," the type also contains the field
// "Name string."
//
// Structural constraints must match *exactly*.
//
// UniqueName *does* satisfy the interface constraint "CanGetName."
type UniqueName struct {
	Unique
	Name string
}

// NewHasT returns a new instance of T.
func NewHasT[T HasID]() T {
	// Declare a new instance of T on the stack.
	var t T

// Return the new T by value.
	return t
}

// NewCanGetT returns a new instance of T.
func NewCanGetT[T CanGetID]() T {
	// Declare a new instance of T on the stack.
	var t T

// Return the new T by value.
	return t
}

func main() {
	fmt.Printf("%T\n", NewCanGetT[UniqueName]())
}

About the Playground

The Go Playground is a web service that runs on golang.org's servers. The service receives a Go program, vets, compiles, links, and runs the program inside a sandbox, then returns the output.

If the program contains tests or examples and no main function, the service runs the tests. Benchmarks will likely not be supported since the program runs in a sandboxed environment with limited resources.

There are limitations to the programs that can be run in the playground:

The playground can use most of the standard library, with some exceptions. The only communication a playground program has to the outside world is by writing to standard output and standard error.
In the playground the time begins at 2009-11-10 23:00:00 UTC (determining the significance of this date is an exercise for the reader). This makes it easier to cache programs by giving them deterministic output.
There are also limits on execution time and on CPU and memory usage.

The article "Inside the Go Playground" describes how the playground is implemented. The source code is available at https://go.googlesource.com/playground.

This playground uses a development version of Go.
The current version is devel go1.24-b68f8ca89a Sat Nov 23 01:41:58 2024 +0000.

The playground service is used by more than just the official Go project (Go by Example is one other instance) and we are happy for you to use it on your own site. All we ask is that you contact us first (note this is a public mailing list), use a unique user agent in your requests (so we can identify you), and that your service is of benefit to the Go community.

Any requests for content removal should be directed to security@golang.org. Please include the URL and the reason for the request.