Go Methods

In Go, methods are functions which are associated with some type; this type is called Receiver Type and methods are often called Receiver Functions. Their format is:

func (rcv RcvT) foo(arg1 TArg1, arg2 TArg2, ...) RtnT {

   ...

   // use rcv

}

This example shows some interesting properties of methods:

package main

import "fmt"

type MyInt struct {

i int

}

// associate function to a structure

// *MyInt is a Receiver type (here, it's a pointer type)

// multiply is now a Receiver function. From now on it requires a receiver in order to be called: (*MyInt).multiply

// When called on MyInt instance pointer, a copy of that pointer is passed to this function.

func (mi *MyInt) multiply(i int) {

mi.i = mi.i * i

}

// Receiver type can also be a value type.

// From now on it requires a receiver in order to be called: (MyInt).multiply

// When called on MyInt instance, a copy of that object is passed to this function.

func (mi MyInt) add(i int) {

mi.i = mi.i + i

}

func assign_struct_function_to_var(mi *MyInt) {

// Although function variable does not mention Receiver type...

var f func(i int)

// ...we can assign Receiver function to it!

f = mi.multiply

f(2)

fmt.Printf("%d\n", mi.i)

// function associated to struct can't be used in assignments on its own

// error:

// undefined: multiply

// f = multiply

}

func main() {

mi := MyInt{}

mi.i = 1

fmt.Printf("%d\n", mi.i)

// function associated to struct can't be invoked on its own

// error:

// undefined: multiply

// multiply(2)

assign_struct_function_to_var(&mi)

}