Learning Go interfaces

interfaces.go

package main

import "fmt"

type IFace interface {
	Method() string
}

func TakingObject(i IFace) {
	fmt.Println(i.Method())
}

func TakingPointer(p *IFace) {
	fmt.Println((*p).Method())
	// fmt.Println(p.Method()) --> compilation error: p.Method undefined (type *IFace is pointer to interface, not interface)
}

type Foo struct {
	C int
}

func (f Foo) Method() string {
	f.C += 1
	return fmt.Sprintf("Foo: plain: %d", f.C)
}

type Bar struct {
	C int
}

func (b *Bar) Method() string {
	b.C += 1
	return fmt.Sprintf("Bar: pointer %d", b.C)
}

func main() {
	f1 := Foo{}
	// f1 is copied when transmitted to func
	TakingObject(f1) // -> Foo: plain: 1
	TakingObject(f1) // -> Foo: plain: 1
	// TakingPointer(f1) --> compilation error: cannot use f1 (type Foo) as type *IFace in argument to TakingPointer:
	//                                         *IFace is pointer to interface, not interface
	TakingObject(&f1) // -> Foo: plain: 1
	TakingObject(&f1) // -> Foo: plain: 1
	// TakingPointer(&f1) --> compilation error: cannot use &f1 (type *Foo) as type *IFace in argument to TakingPointer:
	//                                          *IFace is pointer to interface, not interface

	b1 := Bar{}
	// TakingObject(b1) --> compilation error: cannot use b1 (type Bar) as type IFace in argument to TakingObject:
	//                                         Bar does not implement IFace (Method method has pointer receiver)
	// TakingPointer(b1) --> compilation error: cannot use b1 (type Bar) as type *IFace in argument to TakingPointer:
	//                                         *IFace is pointer to interface, not interface

	TakingObject(&b1) // -> Bar: pointer 1
	TakingObject(&b1) // -> Bar: pointer 2
	// TakingPointer(&b1) --> compilation error: cannot use &b1 (type *Bar) as type *IFace in argument to TakingPointer:
	//                                          *IFace is pointer to interface, not interface
}