CODEWITHSUNDEEP
goconstructorinit
pretty08
pretty08

Reputation: 157

What is the best way to implement a constructor/init methods in Go

I have a program as below:

package main

//Define declare variables
type Define struct {
    len    int
    breath int
}

//Area calculate area
func (e *Define) Area() (a int) {
    a = e.len * e.breath
    return a
}

I call the above program in:

package main

func main() {
    y := Define{10, 10}
    x := y.Area()
    print(x)
}

I would like make the function Area() as part of struct initialization. Currently, I have to create a new object for "Define" ie "y" and then call the method Area. Instead is there a way that Area methods auto calculates once I create the object?

Upvotes: 3

Views: 5104

Answers (2)

dm03514
dm03514

Reputation: 55952

Go has the concept of "Constructors" that may cover your use case. Combined with exporting it allows you to encapsulate initialization by hiding specifics of calculation from callers:

package main

//Define declare variables
type Define struct {
    len    int
    breath int
    area   int 
}

func (e Define) Area() int {
    return e.area
}

func NewDefine(l, b int) Define {
   d := Define{
      len: l,
      breath: b,
      area: calculateArea(l, b),
   }
   return d
}

The pattern to focus on is the exported NewX. It is extremely common to see constructors named NewX which will initialize and return a struct. The above delegates to an un-exported calculateArea function. Of course there are many different possible ways for you to structure your program. calculateArea still encapsulates the area calculation for trivial unit testing, while hiding it from callers by not exporting it.

Upvotes: 0

Metatrix
Metatrix

Reputation: 279

I'd rename Define to something better like Geometry. Usually in Golang, New... is used as a "constructor"

Since you said you wanted area to be autocalculated, include the area as a struct field. Here's how I'd go about it (https://play.golang.org/p/4y6UVTTT34Z):

package main

//variables
type Geometry struct {
    len    int
    breath int
    area   int
}

// Constructor
func NewGeometry(len int, breadth int) *Geometry {
    g := &Geometry{len, breadth, Area(len, breadth)}
    return g
}

//Area calculate area
func Area(len, breadth int) (a int) {
    return len * breadth
}

func main() {
    g := NewGeometry(10, 2)
    fmt.Println(g.area)
}

Upvotes: 4

Related Questions