add: money type to interfaces

interfaces/01-methods/book.go

@@ -16,7 +16,7 @@ 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)
+	fmt.Printf("%-15s: $%.2f\n", b.title, b.price)
 }
 
 // ----------------------------------------------------------------------------
@@ -25,12 +25,12 @@ func (b book) print() {
 //
 // func (b book) printBook() {
 // 	// b is a copy of the original `book` value here.
-// 	fmt.Printf("%-15s: $%.2f \n", b.title, b.price)
+// 	fmt.Printf("%-15s: $%.2f\n", b.title, b.price)
 // }
 
 // ----------------------------------------------------------------------------
 // b is a copy of the original `book` value here.
 //
 // func printBook(b book) {
-// 	fmt.Printf("%-15s: $%.2f \n", b.title, b.price)
+// 	fmt.Printf("%-15s: $%.2f\n", b.title, b.price)
 // }

interfaces/02-receivers/book.go

@@ -15,5 +15,5 @@ type book struct {
 }
 
 func (b book) print() {
-	fmt.Printf("%-15s: $%.2f \n", b.title, b.price)
+	fmt.Printf("%-15s: $%.2f\n", b.title, b.price)
 }

interfaces/03-nonstructs/book.go

@@ -11,10 +11,9 @@ import "fmt"
 
 type book struct {
 	title string
-	price float64
+	price money
 }
 
 func (b book) print() {
-	// b is a copy of the original `book` value here.
-	fmt.Printf("%-15s: $%.2f \n", b.title, b.price)
+	fmt.Printf("%-15s: %s\n", b.title, b.price.string())
 }

interfaces/03-nonstructs/game.go

@@ -11,24 +11,13 @@ import "fmt"
 
 type game struct {
 	title string
-	price float64
+	price money
 }
 
 func (g *game) print() {
-	fmt.Printf("%-15s: $%.2f\n", g.title, g.price)
+	fmt.Printf("%-15s: %s\n", g.title, g.price.string())
 }
 
-// + discount gets a copy of `*game`.
-// + discount can update the original `game` through the game pointer.
-// + it's better to use the same receiver type: `*game` for all methods.
 func (g *game) discount(ratio float64) {
-	g.price *= (1 - ratio)
+	g.price *= money(1 - ratio)
 }
-
-// PREVIOUS CODE:
-
-// ----------------------------------------------------------------------------
-// + `g` is a copy: `discount` cannot change the original `g`.
-// func (g game) discount(ratio float64) {
-// 	g.price *= (1 - ratio)
-// }

interfaces/03-nonstructs/list.go

@@ -9,9 +9,9 @@ package main
 
 import "fmt"
 
-// + you can attach methods to any concrete type.
+// + you can attach methods to non-struct types.
 // + rule: you need to declare a new type in the same package.
-type list []game
+type list []*game
 
 func (l list) print() {
 	// `list` acts like a `[]game`

interfaces/03-nonstructs/main.go

@@ -14,14 +14,15 @@ func main() {
 		tetris    = game{title: "tetris", price: 5}
 	)
 
-	var items []game
-	items = append(items, minecraft, tetris)
+	var items []*game
+	items = append(items, &minecraft, &tetris)
 
 	// you can attach methods to a compatible type on the fly:
-	my := list([]game{minecraft, tetris})
-
-	// you can call methods even on a nil value
+	// items -> []*game
+	// list  -> []*game
+	my := list(items)
 	// my = nil
 
-	my.print() // or: list.print(items)
+	// you can call methods even on a nil value
+	my.print()
 }

interfaces/03-nonstructs/money.go

@@ -0,0 +1,17 @@
+// 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 money float64
+
+func (m money) string() string {
+	// $xx.yy
+	return fmt.Sprintf("$%.2f", m)
+}

interfaces/04-interfaces/book.go

@@ -11,9 +11,9 @@ import "fmt"
 
 type book struct {
 	title string
-	price float64
+	price money
 }
 
 func (b book) print() {
-	fmt.Printf("%-15s: $%.2f \n", b.title, b.price)
+	fmt.Printf("%-15s: %s\n", b.title, b.price.string())
 }

interfaces/04-interfaces/game.go

@@ -11,13 +11,13 @@ import "fmt"
 
 type game struct {
 	title string
-	price float64
+	price money
 }
 
 func (g *game) print() {
-	fmt.Printf("%-15s: $%.2f\n", g.title, g.price)
+	fmt.Printf("%-15s: %s\n", g.title, g.price.string())
 }
 
 func (g *game) discount(ratio float64) {
-	g.price *= (1 - ratio)
+	g.price *= money(1 - ratio)
 }

interfaces/04-interfaces/money.go

@@ -0,0 +1,16 @@
+// 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 money float64
+
+func (m money) string() string {
+	return fmt.Sprintf("$%.2f", m)
+}

interfaces/04-interfaces/puzzle.go

@@ -11,9 +11,9 @@ import "fmt"
 
 type puzzle struct {
 	title string
-	price float64
+	price money
 }
 
 func (p puzzle) print() {
-	fmt.Printf("%-15s: $%.2f \n", p.title, p.price)
+	fmt.Printf("%-15s: %s\n", p.title, p.price.string())
 }

interfaces/05-assertion/book.go

@@ -11,10 +11,10 @@ import "fmt"
 
 type book struct {
 	title    string
-	price    float64
+	price    money
 	readTime int
 }
 
 func (b book) print() {
-	fmt.Printf("%-15s: $%.2f \n", b.title, b.price)
+	fmt.Printf("%-15s: %s\n", b.title, b.price.string())
 }

interfaces/05-assertion/game.go

@@ -11,14 +11,14 @@ import "fmt"
 
 type game struct {
 	title    string
-	price    float64
+	price    money
 	playTime int
 }
 
 func (g *game) print() {
-	fmt.Printf("%-15s: $%.2f\n", g.title, g.price)
+	fmt.Printf("%-15s: %s\n", g.title, g.price.string())
 }
 
 func (g *game) discount(ratio float64) {
-	g.price *= (1 - ratio)
+	g.price *= money(1 - ratio)
 }

interfaces/05-assertion/money.go

@@ -0,0 +1,16 @@
+// 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 money float64
+
+func (m money) string() string {
+	return fmt.Sprintf("$%.2f", m)
+}

interfaces/05-assertion/puzzle.go

@@ -11,13 +11,13 @@ import "fmt"
 
 type puzzle struct {
 	title string
-	price float64
+	price money
 }
 
 func (p *puzzle) print() {
-	fmt.Printf("%-15s: $%.2f \n", p.title, p.price)
+	fmt.Printf("%-15s: %s\n", p.title, p.price.string())
 }
 
 func (p *puzzle) discount(ratio float64) {
-	p.price *= (1 - ratio)
+	p.price *= money(1 - ratio)
 }

interfaces/06-composition/book.go

@@ -11,15 +11,15 @@ import "fmt"
 
 type book struct {
 	title    string
-	price    float64
+	price    money
 	readTime int
 }
 
 func (b book) print() {
-	fmt.Printf("%-15s: $%.2f \n", b.title, b.price)
+	fmt.Printf("%-15s: %s\n", b.title, b.price.string())
 }
 
 // TODO: NEW
-func (b book) sum() float64 {
+func (b book) sum() money {
 	return b.price
 }

interfaces/06-composition/game.go

@@ -11,12 +11,12 @@ import "fmt"
 
 type game struct {
 	title    string
-	price    float64
+	price    money
 	playTime int
 }
 
 func (g *game) print() {
-	fmt.Printf("%-15s: $%.2f\n", g.title, g.price)
+	fmt.Printf("%-15s: %s\n", g.title, g.price.string())
 }
 
 // func (g *game) String() string {
@@ -24,10 +24,10 @@ func (g *game) print() {
 // }
 
 func (g *game) discount(ratio float64) {
-	g.price *= (1 - ratio)
+	g.price *= money(1 - ratio)
 }
 
 // TODO: NEW
-func (g *game) sum() float64 {
+func (g *game) sum() money {
 	return g.price
 }

interfaces/06-composition/list.go

@@ -26,7 +26,7 @@ func (l list) print() {
 }
 
 // TODO: NEW
-func (l list) sum() (n float64) {
+func (l list) sum() (n money) {
 	for _, it := range l {
 		n += it.sum()
 	}

interfaces/06-composition/money.go

@@ -0,0 +1,16 @@
+// 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 money float64
+
+func (m money) string() string {
+	return fmt.Sprintf("$%.2f", m)
+}

interfaces/06-composition/puzzle.go

@@ -11,14 +11,14 @@ import "fmt"
 
 type puzzle struct {
 	title string
-	price float64
+	price money
 }
 
 func (p puzzle) print() {
-	fmt.Printf("%-15s: $%.2f \n", p.title, p.price)
+	fmt.Printf("%-15s: %s\n", p.title, p.price.string())
 }
 
 // TODO: NEW
-func (p puzzle) sum() float64 {
+func (p puzzle) sum() money {
 	return p.price
 }

interfaces/06-composition/types.go

@@ -10,7 +10,7 @@ type printer interface {
 
 // TODO: NEW
 type summer interface {
-	sum() float64
+	sum() money
 }
 
 // TODO: NEW