Method declaration

Learn to declare methods on structs.

Defining methods

A method is a function bound to a specific type. The receiver is written in parentheses between func and the name:

type Dikdortgen struct{ En, Boy float64 }

func (d Dikdortgen) Alan() float64 {
    return d.En * d.Boy
}

r := Dikdortgen{3, 4}
fmt.Println(r.Alan())  // 12

The receiver name is usually the type's initial (d); this or self isn't used.

Method or function?

If an operation is directly about a type's data, writing it as a method improves readability: r.Alan() is clearer than Alan(r). Methods are also how interfaces are satisfied (you'll see later). Method values can be passed around like functions too: f := r.Alan; f().

Exercise Area and perimeter

Write the Alan() and Cevre() methods for Dikdortgen (En, Boy float64). Print both for Dikdortgen{3, 4} on one line.

Show example solution

package main

import "fmt"

type Dikdortgen struct{ En, Boy float64 }

func (d Dikdortgen) Alan() float64  { return d.En * d.Boy }
func (d Dikdortgen) Cevre() float64 { return 2 * (d.En + d.Boy) }

func main() {
    r := Dikdortgen{3, 4}
    fmt.Println(r.Alan(), r.Cevre())
}

Test yourself

Which types can have methods added?
- Only interfaces
- Any type defined in the same package
- Only structs
- Built-in types like int directly too
Show answer

Any type defined in the same package — You can add methods to any type you define, like type Puan int; you can't add them directly to another package's type (e.g. int, time.Time).

Receiver

func (____ Dikdortgen) Cevre() float64 {
    return 2 * (d.En + d.Boy)
}

Show answer

func (d Dikdortgen) Cevre() float64 {
    return 2 * (d.En + d.Boy)
}

Part

(d Dikdortgen)

Receiver
Alan

Method name
r.Alan()

Method call
f := r.Alan

Method value

Next lesson: Pointer receiver

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