Go to Go - Struct and Methods

Go has a speciel type struct to define custome type with named fields. Struct act like collection of attributes/properties similar to classes in OOPS languages out there, but not exactly.

Structs

Struct can have named attributes of any type and methods can be defined to operate on that. Lets define a Person struct that will contain first_name, last_name and age

type Person struct{
  first_name, last_name string
  age uint8
}

So that’s it, we just defined a person struct with some attributes. Let’s use it. There are many way to initialize an struct, here are some

var p Person

Note when we initialize it without providing any value, go assign default value to each attributes, depending on there types, like first_name, last_name will be assigned a blank string “” and age will be assigned 0.

This can also be in initialized using new function that allocates memory and return pointer.

p := new(Person)

But most used way is to initialize while passing values to it, here is how

p := Person{first_name: "John", last_name: "Lego", age: "32"}
//or we can leave off attribute names if we know order
p := Person{"John", "Lego", "32"}
Methods

In Go, Methods are similar to func except that they have a receiver to operate on. To get full_name of a person we would love to define a method to Person struct like

func(p Person) full_name() {
  fmt.Println(p.first_name, p.last_name)
}
p.full_name()
//=> "John Lego"

Well done Jack! But problem with this method is, it is printing full_name to standard output. But in real world we would need our full_name to return full name of a person. Here is how

func(p Person) full_name() string {
  s := p.first_name + " " + p.last_name
  return s
}
fmt.Println(p.full_name())
//=> "John Lego"

Just FYI Jack, struct can also have embedded types, not just legacy types. Here is an example of struct Employee

type Employee struct{
  Person
  employee_id string
}

Now to initilize it we need to follow same way, but first argument should be of type person, like

e :=  Employee{Person{"Pankaj", "Bagwan", 26}, "emp101"}
fmt.Println(e.Person.full_name())
fmt.Println(e.full_name())
fmt.Println(e.employee_id)

Note that method defined on struct Person is alo available directly and indirectly to employee.

Happy Structing :)