George  Koelpin

George Koelpin

1597383720

Copying Interface Values In Go

I am constantly thinking about the Go language and how things work. Lately I have been thinking how everything in Go is by value. We see this when we pass values to functions, when we iterate over slices and when we perform type assertions. In every case, copies of the values that are stored in these data structures are returned. When I first started learning Go this threw me off, but I have come to appreciate the reasonability this brings to our code.

I started to question what would happen if I made a copy of an interface value that was storing a value and not a pointer. Would each new interface value get their own copy or would they share the value? To get a definitive answer I wrote a small program to inspect the interface value.

https://play.golang.org/p/KXvtpd9_29

Listing 1

06 package main
07
08 import (
09     "fmt"
10     "unsafe"
11 )
12  
13 // notifier provides support for notifying events.
14 type notifier interface {
15     notify()
16 }
17  
18 // user represents a user in the system.
19 type user struct{
20     name string
21 }
22  
23 // notify implements the notifier interface.
24 func (u user) notify() {
25     fmt.Println("Alert", u.name)
26 }

In Listing 1 on line 14 we see the declaration of an interface type named notifier with a single method named notify. Then on line 19 we have the declaration of a concrete type named user with the implementation of the notifier interface on line 24. We now have an interface and a concrete type to work with.

Listing 2

28 // inspect allows us to look at the value stored
29 // inside the interface value.
30 func inspect(n *notifier, u *user) {
31     word := uintptr(unsafe.Pointer(n)) + uintptr(unsafe.Sizeof(&u))
32     value := (**user)(unsafe.Pointer(word))
33     fmt.Printf("Addr User: %p  Word Value: %p  Ptr Value: %v\n", u, *value, **value)
34 }

In Listing 2 we have the inspect function that starts on line 30. This function gives us a pointer to the second word of the interface value. With this pointer we can inspect the value of the second word of the interface and the user value that the second word points to. We need to review these values to really understand the mechanics of the interface.

Listing 3

36 func main() {
37
38     // Create a notifier interface and concrete type value.
39     var n1 notifier
40     u := user{"bill"}
41
42     // Store a copy of the user value inside the notifier
43     // interface value.
44     n1 = u
45
46     // We see the interface has its own copy.
47     // Addr User: 0x1040a120  Word Value: 0x10427f70  Ptr Value: {bill}
48     inspect(&n1, &u)
49
50     // Make a copy of the interface value.
51     n2 := n1
52 	
53     // We see the interface is sharing the same value stored in
54     // the n1 interface value.
55     // Addr User: 0x1040a120  Word Value: 0x10427f70  Ptr Value: {bill}
56     inspect(&n2, &u)
57
58     // Store a copy of the user address value inside the
59     // notifier interface value.
60     n1 = &u
61
62     // We see the interface is sharing the u variables value
63     // directly. There is no copy.
64     // Addr User: 0x1040a120  Word Value: 0x1040a120  Ptr Value: {bill}
65     inspect(&n1, &u)
66 }

Listing 3 shows the main function which starts on line 36. The very first thing we do on line 39 is declare a variable named n1 of interface type notifier set to its zero value. Then on line 40 we declare a variable named u of type user set with the string “bill”.

#go

What is GEEK

Buddha Community

Copying Interface Values In Go
Fannie  Zemlak

Fannie Zemlak

1599854400

What's new in the go 1.15

Go announced Go 1.15 version on 11 Aug 2020. Highlighted updates and features include Substantial improvements to the Go linker, Improved allocation for small objects at high core counts, X.509 CommonName deprecation, GOPROXY supports skipping proxies that return errors, New embedded tzdata package, Several Core Library improvements and more.

As Go promise for maintaining backward compatibility. After upgrading to the latest Go 1.15 version, almost all existing Golang applications or programs continue to compile and run as older Golang version.

#go #golang #go 1.15 #go features #go improvement #go package #go new features

Zakary  Goyette

Zakary Goyette

1596928740

When an Interface Depends on Another Interface in Go

Interfaces are the way for you to describe abstract behaviour, but what makes Go Interfaces so great? Well, it’s probably the first thing you learn about them, that they are implemented implicitly. You don’t need to explicitly specify about a type which interface it implements. This makes dependancy injection super easy in Go, leaving your code decoupled. You are defining the behaviour you need, and not what you do. Your type could implement more and more interfaces, without ever changing your code!

But when an interface depends on another one, you encounter a type dependancy, and not a behaviour one. In this post we’ll try to see why and how to handle this case.

When an interface is just a type.

So for a type to implement an interface, it must have all the interface’s methods. This means the methods’ names and signatures. Each method must take and return the exactly same type parameters. This strictness stays even if that parameter type is an interface.

Example

Imagine we have an application for running jobs. We want to separate the implementation of the job and the way the job runs.

For doing the job we will define a Worker interface, and for running the job we will define a Runner interface. Then we will compose these two interfaces in a separated package called runner :

package runner

	type Worker interface {
	  Do()
	}

	type Runner interface {
	  Run(Worker)
	}

	func Run(r Runner, w Worker) {
	  r.Run(w)
	}

So the package runner doesn’t do much except exporting a function for running a Worker. It doesn’t know anything about what the job is and how does it run.

#go #dependencies #golang #interfaces

George  Koelpin

George Koelpin

1597383720

Copying Interface Values In Go

I am constantly thinking about the Go language and how things work. Lately I have been thinking how everything in Go is by value. We see this when we pass values to functions, when we iterate over slices and when we perform type assertions. In every case, copies of the values that are stored in these data structures are returned. When I first started learning Go this threw me off, but I have come to appreciate the reasonability this brings to our code.

I started to question what would happen if I made a copy of an interface value that was storing a value and not a pointer. Would each new interface value get their own copy or would they share the value? To get a definitive answer I wrote a small program to inspect the interface value.

https://play.golang.org/p/KXvtpd9_29

Listing 1

06 package main
07
08 import (
09     "fmt"
10     "unsafe"
11 )
12  
13 // notifier provides support for notifying events.
14 type notifier interface {
15     notify()
16 }
17  
18 // user represents a user in the system.
19 type user struct{
20     name string
21 }
22  
23 // notify implements the notifier interface.
24 func (u user) notify() {
25     fmt.Println("Alert", u.name)
26 }

In Listing 1 on line 14 we see the declaration of an interface type named notifier with a single method named notify. Then on line 19 we have the declaration of a concrete type named user with the implementation of the notifier interface on line 24. We now have an interface and a concrete type to work with.

Listing 2

28 // inspect allows us to look at the value stored
29 // inside the interface value.
30 func inspect(n *notifier, u *user) {
31     word := uintptr(unsafe.Pointer(n)) + uintptr(unsafe.Sizeof(&u))
32     value := (**user)(unsafe.Pointer(word))
33     fmt.Printf("Addr User: %p  Word Value: %p  Ptr Value: %v\n", u, *value, **value)
34 }

In Listing 2 we have the inspect function that starts on line 30. This function gives us a pointer to the second word of the interface value. With this pointer we can inspect the value of the second word of the interface and the user value that the second word points to. We need to review these values to really understand the mechanics of the interface.

Listing 3

36 func main() {
37
38     // Create a notifier interface and concrete type value.
39     var n1 notifier
40     u := user{"bill"}
41
42     // Store a copy of the user value inside the notifier
43     // interface value.
44     n1 = u
45
46     // We see the interface has its own copy.
47     // Addr User: 0x1040a120  Word Value: 0x10427f70  Ptr Value: {bill}
48     inspect(&n1, &u)
49
50     // Make a copy of the interface value.
51     n2 := n1
52 	
53     // We see the interface is sharing the same value stored in
54     // the n1 interface value.
55     // Addr User: 0x1040a120  Word Value: 0x10427f70  Ptr Value: {bill}
56     inspect(&n2, &u)
57
58     // Store a copy of the user address value inside the
59     // notifier interface value.
60     n1 = &u
61
62     // We see the interface is sharing the u variables value
63     // directly. There is no copy.
64     // Addr User: 0x1040a120  Word Value: 0x1040a120  Ptr Value: {bill}
65     inspect(&n1, &u)
66 }

Listing 3 shows the main function which starts on line 36. The very first thing we do on line 39 is declare a variable named n1 of interface type notifier set to its zero value. Then on line 40 we declare a variable named u of type user set with the string “bill”.

#go

Neal  Bode

Neal Bode

1599306000

Golang Interface Example | Interface Implementation in Go

Golang interface is a type defined using a set of method signatures. It describes the behavior of a similar kind of objects. A Go interface is a type that consists of the collection of method signatures.

If you are new to Go language then, you may be heard or seen in the code about interface{} a lot in code snippets and tutorials.  This can be very daunting seeing this at first. Interface implementation is one of the core concepts of Object-oriented programming language.

If you have used Java, PHP, or Python then you might know what interface is and how it can be useful to build a scalable application.

An interface is a type defined using a set of method signatures. It describes the behavior of a similar kind of objects. Go programming provides another data type called interfaces which represents a set of method signatures.

The struct data type implements these interfaces to have method definitions for the method signature of the interfaces.

#golang #go #golang interface #php #java #python

Zander  Herzog

Zander Herzog

1596793260

Secure HTTPS servers in Go

In this article, we are going to look at some of the basic APIs of the http package to create and initialize HTTPS servers in Go.

Image for post

(source: unsplash.com)

In the “Simple Hello World Server” lesson, we learned about net/http package, how to create routes and how [ServeMux](https://golang.org/pkg/net/http/#ServeMux) works. In the “Running multiple HTTP servers” lesson, we learned about [Server](https://golang.org/pkg/net/http/#Server) structure and how to run multiple HTTP servers concurrently.

In this lesson, we are going to create an HTTPS server using both Go’s standard server configuration and custom configuration (using [_Server_](https://golang.org/pkg/net/http/#Server) structure). But before this, we need to know what HTTPS really is?

HTTPS is a big topic of discussion in itself. Hence while writing this lesson, I published an article just on “How HTTPS works?”. I advise you to read this lesson first before continuing this article. In this article, I’ve also described the encryption paradigm and SSL certificates generation process.


If we recall the simplest HTTP server example from previous lessons, we only need http.``[ListenAndServe](https://golang.org/pkg/net/http/#ListenAndServe) function to start an HTTP server and http.``[HandleFunc](https://golang.org/pkg/net/http/#HandleFunc) to register a response handler for a particular endpoint.

Image for post

(https://play.golang.org/p/t3sOenOYAzS)

In the example above, when we run the command go run server.go , it will start an HTTP server on port 9000. By visiting http://localhost:9000 URL in a browser, you will be able to see a Hello World! message on the screen.

Image for post

(http://localhost:9000)

As we know, the nil argument to ListenAndServe() call invokes Go to use the [DefaultServeMux](https://golang.org/pkg/net/http/#DefaultServeMux) response multiplexer, which is the default instance of ServeMux structure provided globally by the Go. The HandleFunc() call adds a response handler for a specific route on the multiplexer instance.

The http.ListenAndServe() call uses the Go’s standard HTTP server configuration, however, in the previous lesson, how we can customize a server using [Server](https://golang.org/pkg/net/http/#Server) structure type.

To start an HTTPS server, all we need do is to call ServerAndListenTLS method with some configuration. Just like ServeAndListen method, this method is available on both the http package and the Server structure.

The http.``[ServeAndListenTLS](https://golang.org/pkg/net/http/#ListenAndServeTLS) method uses the Go’s standard server implementation, however, both [Server](https://golang.org/pkg/net/http/#Server) instance and Server.``[ServeAndListenTLS](https://golang.org/pkg/net/http/#Server.ListenAndServeTLS) method can be configured for our needs.

#go-programming-language #go #golang-tutorial #go-programming #golang