Maps

2moretypes/maps.go

@@ -0,0 +1,67 @@
+package main
+
+import (
+	"fmt"
+	"reflect"
+)
+
+type FavoriteNumbers struct {
+	num1, num2, num3 int
+}
+
+func main() {
+	fmt.Println("Map, maps keys to values")
+	fmt.Println("Zero value of a map is nil")
+	fmt.Println("make function return a map of the given type, initialized and ready for use")
+
+	m := make(map[string]FavoriteNumbers)
+	/* or:
+	var m map[string]FavoriteNumbers // Even if you declared map with this line, you must use make to initialize map
+	m = make(map[string]FavoriteNumbers)
+	*/
+	m["Aliberk"] = FavoriteNumbers{1, 2, 3}
+	m["Deniz"] = FavoriteNumbers{4, 5, 6}
+
+	fmt.Println(m["Aliberk"])
+
+	var map2 map[int]int
+	// map2[5] = 1 // Runtime error without make: "panic: assignment to entry in nil map"
+
+	map2 = make(map[int]int)
+
+	map2[1] = 3
+	// map2["2"] = 1 // Compile error
+	map2['3'] = 1 // not 3, 51 (ASCII value)
+
+	fmt.Println(map2[5]) // any other non-declared value is zero
+	fmt.Println(map2[1])
+	fmt.Println(map2[3])  // 0
+	fmt.Println(map2[51]) // 1
+	fmt.Println(map2)
+
+	fmt.Printf("\nYou can also use Map Literals for assigning values directly, but keys are required!\n")
+
+	map3 := map[string]FavoriteNumbers{
+		"Prime":  FavoriteNumbers{2, 3, 5}, // FavoriteNumbers are not necessary in there
+		"bigger": {123, 124, 125},
+	}
+	fmt.Println(map3)
+	fmt.Println(reflect.TypeOf(map3).Kind())
+	fmt.Println(reflect.TypeOf(map3["Prime"]).Kind())
+	fmt.Println(reflect.TypeOf(map3["Prime"].num1).Kind())
+
+	fmt.Printf("\n\n%p\n", map3)
+	fmt.Printf("%p\n", &map3)
+
+	fmt.Printf("\nElements can be deleted with delete function:\n")
+	delete(map3, "bigger")
+	fmt.Println(map3)
+
+	fmt.Println("Also Elements can be tested like this:")
+	elem, ok := map3["bigger"]
+	fmt.Println(elem, ok)
+
+	elem, ok = map3["Prime"]
+	fmt.Println(elem, ok)
+
+}

exercises/maps.go

@@ -0,0 +1,20 @@
+package main
+
+// Exercise: https://go.dev/tour/moretypes/23
+
+import (
+	//"golang.org/x/tour/wc" // Not valid in local!
+	"strings"
+)
+
+func WordCount(s string) map[string]int {
+	m := make(map[string]int)
+	for _, val := range strings.Fields(s) {
+		m[val] += 1
+	}
+	return m
+}
+
+func main() {
+	// wc.Test(WordCount)
+}