add ch12_3

ch12/3/ch12_3.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"fmt"
+	"math"
+	"sync"
+)
+
+func CreateSqrtMap() map[int]float64 {
+	numKeys := 100_000
+	newMap := make(map[int]float64)
+
+	for i := range numKeys {
+		newMap[i] = math.Sqrt(float64(i))
+	}
+	return newMap
+}
+
+var initCreateMapSqrt func() map[int]float64 = sync.OnceValue(CreateSqrtMap)
+
+func main() {
+	sqrtMap := initCreateMapSqrt()
+	n := 100_000 / 1_000
+	for i := range n {
+		keyVal := i * 1_000
+		fmt.Printf("Value of map by key[%d]: %f\n", keyVal, sqrtMap[keyVal])
+	}
+}

ch12/3/go.mod

@@ -0,0 +1,3 @@
+module gitea.local.lab/Lbenedar/learning_go/ch12/3
+
+go 1.25.0