add: slice internals backing array and slice header

16-slices/exercises/16-internals-backing-array-fix/main.go

@@ -0,0 +1,60 @@
+// 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"
+	"math/rand"
+	"time"
+)
+
+// ---------------------------------------------------------
+// EXERCISE: Fix the backing array problem
+//
+//  You receive numbers from an API. After you're done working
+//  with it, the API needs to continue using those numbers.
+//
+//  But your program changes the numbers (changes the API's slice).
+//
+//  Fix the program so that your program doesn't modify
+//  the original numbers.
+//
+//
+// RESTRICTION
+//
+//  Fix your problem only in the designated area of the code below.
+//
+//
+// EXPECTED OUTPUT
+//
+//  Mine         : [-50 -100 -150]
+//  Original nums: [56 89 15]
+//
+//  Note: Original nums may vary (they're random)
+//        But your slice should look like the above (mine slice)
+//
+//        Yes, it should output only three numbers for the both slices!
+//
+// ---------------------------------------------------------
+
+func main() {
+	// API returns random numbers in an int slice
+	rand.Seed(time.Now().UnixNano())
+	nums := rand.Perm(100)
+
+	// ----------------------------------------
+	// RESTRICTIONS — ONLY ADD YOUR CODE HERE
+	//
+	mine := nums
+	//
+	// ----------------------------------------
+
+	mine[0], mine[1], mine[2] = -50, -100, -150
+	fmt.Println("Mine         :", mine)
+	fmt.Println("Original nums:", nums[:3])
+}

16-slices/exercises/16-internals-backing-array-fix/solution/main.go

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+// 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"
+	"math/rand"
+	"time"
+)
+
+func main() {
+	rand.Seed(time.Now().UnixNano())
+	nums := rand.Perm(100)
+
+	// ----------------------------------------
+	// breaks the connection:
+	// mine and nums now have different backing arrays
+
+	// verbose solution:
+	// var mine []int
+	// mine = append(mine, nums[:3]...)
+
+	// better solution (almost the same thing):
+	mine := append([]int(nil), nums[:3]...)
+	// ----------------------------------------
+
+	mine[0], mine[1], mine[2] = -50, -100, -150
+	fmt.Println("Mine         :", mine)
+	fmt.Println("Original nums:", nums[:3])
+}