reorganize: interfaces section

interfaces/02-receivers/book.go

@@ -15,6 +15,5 @@ type book struct {
 }
 
 func (b book) print() {
-	// b is a copy of the original `book` value here.
 	fmt.Printf("%-15s: $%.2f \n", b.title, b.price)
 }

interfaces/02-receivers/game.go

@@ -14,6 +14,9 @@ type game struct {
 	price float64
 }
 
+// be consistent:
+// if another method in the same type has a pointer receiver,
+// use pointer receivers on the other methods as well.
 func (g *game) print() {
 	fmt.Printf("%-15s: $%.2f\n", g.title, g.price)
 }
@@ -27,8 +30,7 @@ func (g *game) discount(ratio float64) {
 
 // PREVIOUS CODE:
 
-// ----------------------------------------------------------------------------
 // + `g` is a copy: `discount` cannot change the original `g`.
-// func (g game) discount(ratio float64) {
+// func (g *game) discount(ratio float64) {
 // 	g.price *= (1 - ratio)
 // }

interfaces/02-receivers/huge.go

@@ -0,0 +1,29 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+)
+
+type huge struct {
+	// about ~200mb
+	games [10000000]game
+}
+
+// only copies a single pointer.
+func (h *huge) addr() {
+	fmt.Printf("%p\n", h)
+}
+
+// each time it is called,
+// the original value will be copied.
+// calling addr() x 10 times = ~2 GB.
+// func (h huge) addr() {
+// 	fmt.Printf("%p\n", &h)
+// }

interfaces/02-receivers/list.go

@@ -1,26 +0,0 @@
-// For more tutorials: https://blog.learngoprogramming.com
-//
-// Copyright © 2018 Inanc Gumus
-// Learn Go Programming Course
-// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
-//
-
-package main
-
-import "fmt"
-
-// + you can attach methods to any concrete type.
-// + rule: you need to declare a new type in the same package.
-type list []game
-
-func (l list) print() {
-	// `list` acts like a `[]game`
-	if len(l) == 0 {
-		fmt.Println("Sorry. Our store is closed. We're waiting for the delivery 🚚.")
-		return
-	}
-
-	for _, it := range l {
-		it.print()
-	}
-}

interfaces/02-receivers/main.go

@@ -9,19 +9,22 @@ package main
 
 func main() {
 	var (
-		// mobydick  = book{title: "moby dick", price: 10}
+		mobydick  = book{title: "moby dick", price: 10}
 		minecraft = game{title: "minecraft", price: 20}
 		tetris    = game{title: "tetris", price: 5}
 	)
 
-	var items []game
-	items = append(items, minecraft, tetris)
+	// sends a pointer of minecraft to the discount method
+	// same as: (&minecraft).discount(.1)
+	minecraft.discount(.1)
 
-	// you can attach methods to a compatible type on the fly:
-	my := list([]game{minecraft, tetris})
+	mobydick.print()
+	minecraft.print()
+	tetris.print()
 
-	// you can call methods even on a nil value
-	// my = nil
-
-	my.print() // or: list.print(items)
+	// creates a variable that occupies 200mb on memory
+	var h huge
+	for i := 0; i < 10; i++ {
+		h.addr()
+	}
 }