Go Structs


Go Structs

In Go, structs are used to store data and related functions. An example might be a struct to represent a User:

type User struct { FirstName string LastName string Email string Age int }

Here we can store a user’s first name, last name, email address, and age. The name of the property is followed by the type of data we want to store. For example, the FirstName property is a string whereas the Age property is an int.

Creating objects

To initialise a new object, we can use the Go shorthand syntax for creating and assigning variables. We can either pass the data in at this point or set the data at a later time:

func main() { type MyInt int64 // Create a user and set both the first and last name properties user1 := User{ FirstName: "John", LastName: "Wick", } // Now we have our user object, we can set the data like this user1.Email = "[email protected]" user1.Age = 30 }

Object methods

Go enables declaring methods to struct types and non struct types. This enables grouping of relevant operations to the data it affects. In this example we will write a method on the User struct to generate the full name of the user and String method on MyInt type to return a String:

func (myint MyInt) String() string { return fmt.Sprintf("%d", myint) } func (u User) FullName() string { return strings.Join([]string{u.FirstName, u.LastName}, " ") }

This method will join the first and last name of the user with a space in between. Calling the method might look like this:

fmt.println(user1.FullName())

Struct Tags

Struct tags are used to modify how encoders handle the data. For example, setting the key names when encoding to JSON:

type User struct { FirstName string `json:"first_name"` LastName string `json:"last_name"` Email string `json:"email"` Age int `json:"age"` }

Exported Data

Structs can contain both exported (public) and unexported (private) properties. This is set by either having an uppercase first letter for exported or a lowercase first letter for unexported. In this example, we will make the email property private:

type User struct { // Exported Data FirstName string LastName string Age int // Unexported Data email string }

Doing this will make the following code throw a compilation error as it is trying to assign value to an unexported property:

user1.email = "[email protected]"

Same principle applies when attempting to read data from an unexported property.

This also applies to methods:

// Exported method. This can be called from anywhere func (u User) Email() { return u.email } // Unexported method. This can only be called by other methods on this struct func (u User) updateLoginCount { // code to update login count... }

Modifying properties via methods

To modify the data of an object from within one of its methods, the object must be a pointer. An example might look like this:

“`go
// SetEmail sets the user’s email address
func (u *User) SetEmail(email string) {
u.email = email
}

// Email accessor
func (u *User) Email() string {
return u.email
}

func main() {
// Creating the user1 pointer
user1 = &User{
FirstName: “John”,
LastName: “Wick”,
}

// Set the user's email address user1.SetEmail("[email protected]") // Access and print the user's email address fmt.println(user1.Email())

}

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