Methods

3methods/methods.go

@@ -0,0 +1,143 @@
+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")
+
+}