go-learning/3methods/methods.go

package main

import (
	"fmt"
	// "math"
	"reflect"
)

type Vertex struct {
	X, Y float64
}

func (v Vertex) Twice() (float64, float64) { // Twice method has a receiver of type Vertex named v
	return (v.X) * 2, (v.Y * 2)
}

func Twice2(v Vertex) (float64, float64) {
	return (v.X) * 2, (v.Y * 2)
}

//func (f float64) Abs() float64 { // ERROR: cannot define new methods on non-local type float64
//return 1.4}

type MyFloat float64 // First declare type
//Then use this type in a method

func (f MyFloat) Abs() float64 {
	if f < 0 {
		return float64(-f)
	}
	return float64(f)
}

func (v Vertex) Mult(f float64) {
	v.X *= f
	v.Y *= f
	fmt.Printf("%p\n", &v)
}

func (v *Vertex) Mult2(f float64) {
	v.X *= f
	v.Y *= f
	fmt.Printf("%p (address of pointer: %p)\n", v, &v)
}

func Mult3(v *Vertex, f float64) {
	v.X *= f
	v.Y *= f
	fmt.Printf("%p (address of pointer: %p)\n", v, &v)
}

func Mult4(v Vertex, f float64) {
	v.X *= f
	v.Y *= f
	fmt.Printf("%p\n", &v)
}
func main() {
	fmt.Println("Go doest not have classes, but you can define methods on types")

	fmt.Println("A method is a function with a special receiver argument")

	fmt.Println("The Receiver appears between func keyword and the method name")

	v := Vertex{10, 15}
	fmt.Println(v.Twice())

	fmt.Println("You can make this with also using regular functions:")

	fmt.Println(Twice2(v))

	fmt.Printf("\n\n")

	fmt.Println("You cannot declare a method with a receiver whose type is defined in another package. Because of that you also cannot use types like int or float64")
	fmt.Println("You can declare a new type for solving this")

	fmt.Printf("\n")

	var x MyFloat = 12
	fmt.Println(x, reflect.TypeOf(x), reflect.TypeOf(x).Kind())

	f := MyFloat(-123.34) // same as `var f MyFloat = 123.34`
	fmt.Println(f.Abs())

	fmt.Printf("\n\n")

	fmt.Println("Also pointers can be used as receivers in methods")
	v2 := Vertex{12, 13}
	fmt.Printf("V2: %p\n", &v2)
	v2.Mult(12)
	fmt.Println(v2)

	fmt.Printf("\n")

	v3 := Vertex{12, 13}
	fmt.Printf("V3: %p\n", &v3)
	v3.Mult2(12)
	// `(&v3).Mult2(12)` // ! ACTUALLY SAME THING
	fmt.Println(v3)

	p := &v3
	fmt.Printf("V3: %p, P: %p, (address of p pointer: %p)\n", &v3, p, &p)
	p.Mult2(2)
	fmt.Println(v3, p) // BOTH CHANGED

	fmt.Printf("\n")
	fmt.Println("Pointers also can be used with functions but we should pass the variables with ampersant")

	v4 := Vertex{12, 13}
	fmt.Printf("V4: %p\n", &v4)
	// Mult3(v4, 4) // ERROR
	Mult3(&v4, 12)
	fmt.Println(v4)

	fmt.Printf("\n")
	fmt.Println("Also we can declare our first value as pointer for avoid using ampersant")

	p2 := &Vertex{12, 13}
	fmt.Printf("P2: %p, (address of p2 pointer: %p)\n", p2, &p2)
	p2.Mult2(2)
	Mult3(p2, 6)
	fmt.Println(p2)

	fmt.Printf("\n\n")
	fmt.Println("We couldn't use addresses while function requires a normal value in functions. But while using as methods pointers renders it values")

	myVar1 := Vertex{1, 2}
	Mult4(myVar1, 2) // OK
	// Mult4(&myVar1, 2) // Compile ERRORr
	fmt.Println(myVar1)

	myPoint1 := &myVar1
	myVar1.Mult(2)   //OK
	myPoint1.Mult(2) //ALSO OK, interpreted as (*myPoint1).Mult(2)
	// SAME WITH (*myPoint1).Mult(2)

	fmt.Println(myVar1)
	fmt.Println(myPoint1)

	fmt.Printf("\n\n")
	fmt.Println("Using pointer receivers provides more efficent way, bcs there is no copy process")
	fmt.Println("We should avoid using values and pointer receivers together")

}