refactor: stringer

interfaces/10-stringer/list.go

@@ -8,7 +8,6 @@
 package main
 
 import (
-	"fmt"
 	"strings"
 )
 
@@ -21,7 +20,10 @@ func (l list) String() string {
 
 	var str strings.Builder
 	for _, p := range l {
-		fmt.Fprintf(&str, "* %s\n", p)
+		// fmt.Printf("* %s\n", p)
+		str.WriteString("* ")
+		str.WriteString(p.String())
+		str.WriteRune('\n')
 	}
 	return str.String()
 }

interfaces/10-stringer/main.go

@@ -10,17 +10,14 @@ package main
 import "fmt"
 
 func main() {
-	// The money type is a stringer.
-	// You don't need to call the String method when printing a value of it.
-	// var pocket money = 10
-	// fmt.Println(pocket)
-
 	l := list{
 		{title: "moby dick", price: 10, released: toTimestamp(118281600)},
 		{title: "odyssey", price: 15, released: toTimestamp("733622400")},
 		{title: "hobbit", price: 25},
 	}
 
+	l.discount(.5)
+
 	// The list is a stringer.
 	// The `fmt.Print` function can print the `l`
 	// by calling `l`'s `String()` method.
@@ -29,4 +26,9 @@ func main() {
 	// detect whether a type is a Stringer:
 	// https://golang.org/src/fmt/print.go#L627
 	fmt.Print(l)
+
+	// The money type is a stringer.
+	// You don't need to call the String method when printing a value of it.
+	// var pocket money = 10
+	// fmt.Println("I have", pocket)
 }

interfaces/10-stringer/money.go

@@ -11,6 +11,8 @@ import "fmt"
 
 type money float64
 
+// String() returns a string representation of money.
+// money is an fmt.Stringer.
 func (m money) String() string {
 	return fmt.Sprintf("$%.2f", m)
 }

interfaces/10-stringer/timestamp.go

@@ -12,22 +12,26 @@ import (
 	"time"
 )
 
-// timestamp stores, formats and automatically prints a timestamp: it's a stringer.
+// timestamp stores, formats and automatically prints a timestamp.
 type timestamp struct {
+	// timestamp anonymously embeds a time.
+	// no need to convert a time value to a timestamp value to use the methods of the time type.
 	time.Time
 }
 
-// String method makes the timestamp an fmt.stringer.
+// String() returns a string representation of timestamp.
+// timestamp is an fmt.Stringer.
 func (ts timestamp) String() string {
-	if ts.IsZero() {
+	if ts.IsZero() { // same as: ts.Time.IsZero()
 		return "unknown"
 	}
 
 	// Mon Jan 2 15:04:05 -0700 MST 2006
 	const layout = "2006/01"
-	return ts.Format(layout)
+	return ts.Format(layout) // same as: ts.Time.Format(layout)
 }
 
+// toTimestamp returns a timestamp value depending on the type of `v`.
 func toTimestamp(v interface{}) (ts timestamp) {
 	var t int
 

interfaces/11-sort/list.go

@@ -8,7 +8,6 @@
 package main
 
 import (
-	"fmt"
 	"sort"
 	"strings"
 )
@@ -23,9 +22,13 @@ func (l list) String() string {
 	}
 
 	sort.Sort(l)
+
 	var str strings.Builder
 	for _, p := range l {
-		fmt.Fprintf(&str, "* %s\n", p)
+		// fmt.Printf("* %s\n", p)
+		str.WriteString("* ")
+		str.WriteString(p.String())
+		str.WriteRune('\n')
 	}
 	return str.String()
 }

interfaces/12-marshaler/list.go

@@ -8,7 +8,6 @@
 package main
 
 import (
-	"fmt"
 	"sort"
 	"strings"
 )
@@ -21,9 +20,13 @@ func (l list) String() string {
 	}
 
 	sort.Sort(l)
+
 	var str strings.Builder
 	for _, p := range l {
-		fmt.Fprintf(&str, "* %s\n", p)
+		// fmt.Printf("* %s\n", p)
+		str.WriteString("* ")
+		str.WriteString(p.String())
+		str.WriteRune('\n')
 	}
 	return str.String()
 }

interfaces/13-io/list.go

@@ -8,7 +8,6 @@
 package main
 
 import (
-	"fmt"
 	"sort"
 	"strings"
 )
@@ -21,9 +20,13 @@ func (l list) String() string {
 	}
 
 	sort.Sort(l)
+
 	var str strings.Builder
 	for _, p := range l {
-		fmt.Fprintf(&str, "* %s\n", p)
+		// fmt.Printf("* %s\n", p)
+		str.WriteString("* ")
+		str.WriteString(p.String())
+		str.WriteRune('\n')
 	}
 	return str.String()
 }

interfaces/14-composition/list.go

@@ -8,7 +8,6 @@
 package main
 
 import (
-	"fmt"
 	"sort"
 	"strings"
 )
@@ -21,9 +20,13 @@ func (l list) String() string {
 	}
 
 	sort.Sort(l)
+
 	var str strings.Builder
 	for _, p := range l {
-		fmt.Fprintf(&str, "* %s\n", p)
+		// fmt.Printf("* %s\n", p)
+		str.WriteString("* ")
+		str.WriteString(p.String())
+		str.WriteRune('\n')
 	}
 	return str.String()
 }