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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 = "john@wick.com"
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 = "john@wick.com"
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:
// 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("john@wick.com")
// Access and print the user's email address
fmt.println(user1.Email())
}