Methods 

Let's say we wrote these functions, and we have defined email as before:

 type email string
 
 func check(a email) { ... }
 func send(a email, msg string) { ... }

Observe that email is always the first type in the function parameters.

Calling the functions look something like this:

e := "john@smith.com"
check(e)
send(e, "Hello World")

We may want to make that into a method of the email type. We can do so as follows:

type email string
 
func (e email) check() { ... }
func (e email) send(msg string) { ... }

(e email) is called the receiver of the method.

Having defined the methods thus, we may then proceed to call them:

e := "john@smith.com"
e.check()
e.send("Hello World")

Observe the difference between the functions and methods. check(e) becomes e.check(). send(e, "Hello World") becomes e.send("Hello World"). What's the difference other than syntactic difference? The answer is, not much.

A method in Go is exactly the same as a function in Go, with the receiver of the method as the first parameter of the function. It is unlike methods of classes in object-oriented programming languages.

So why bother with methods? For one, it solves the expression problem quite neatly. To see how, we'll look at the feature of Go that ties everything together nicely: interfaces.