add: slice adv. ops. exercises

16-slices/exercises/23-limit-the-backing-array-sharing/api/api.go

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+package api
+
+var temps = []int{5, 10, 3, 25, 45, 80, 90}
+
+// Read returns a range of temperature readings beginning from
+// the `start` until to the `stop`.
+func Read(start, stop int) []int {
+	// ----------------------------------------
+	// RESTRICTIONS — ONLY ADD YOUR CODE HERE
+
+	portion := temps[start:stop]
+
+	// ----------------------------------------
+	return portion
+}
+
+// All returns all the temperature readings
+func All() []int {
+	return temps
+}

16-slices/exercises/23-limit-the-backing-array-sharing/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"
+
+	"github.com/inancgumus/learngo/16-slices/exercises/23-limit-the-backing-array-sharing/api"
+)
+
+// ---------------------------------------------------------
+// EXERCISE: Limit the backing array sharing
+//
+//  You've created an API that returns population counts in a country.
+//  To do that, you return an int slice up to some portion of it.
+//
+//  There is a program that uses your API but it appends to the slice
+//  that your API returns. Doing so, overwrites your API's slice's
+//  backing array as well.
+//
+//  Change your API so that it prevents the overwriting when
+//  the client code wants to append to the returned slice from your
+//  API.
+//
+//
+// STEPS
+//
+//   1. Open the code inside the `api/api.go` folder
+//
+//   2. Fix the code there (not here — but run this code after)
+//
+//
+// CURRENT OUTPUT
+//
+//       The following program overwrites the elements incorrectly
+//          You need to change your API to prevent this behavior
+//                           ^ ^
+//                           | |
+//   API's readings: [5 10 3 1 3 80 90]
+//   Your readings : [5 10 3 1 3]
+//
+//
+// EXPECTED OUTPUT
+//
+//   Now the program cannot change the API's original backing array
+//  (beyond the returned capacity) (so the api now owns the control)
+//                           ^  ^
+//                           |  |
+//   API's readings: [5 10 3 25 45 80 90]
+//   Your readings : [5 10 3 1 3]
+//
+// ---------------------------------------------------------
+
+func main() {
+	// DO NOT TOUCH THE FOLLOWING CODE
+	// THIS IS THE CLIENT PROGRAM THAT USES YOUR API
+	// YOU CANNOT CONTROL IT! :)
+
+	// reads the first three temperatures
+	temps := api.Read(0, 3)
+
+	// appends two new temperature readings
+	temps = append(temps, []int{1, 3}...)
+
+	// prints the current temperatures
+	fmt.Println("API's readings:", api.All())
+	fmt.Println("Your readings :", temps)
+}

16-slices/exercises/23-limit-the-backing-array-sharing/solution/api/api.go

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+package api
+
+var temps = []int{5, 10, 3, 25, 45, 80, 90}
+
+// Read returns a range of temperature readings beginning from
+// the `start` until to the `stop`.
+func Read(start, stop int) []int {
+	// Uses a full slice expression to control the length of the
+	// backing array (or the capacity of the returned slice).
+	//
+	// So the next append allocates a new backing array, which
+	// in turn doesn't overwrite the temps slice's backing array.
+	//                           ^^
+	//                           ||
+	//                          /  \
+	//                         |    |
+	portion := temps[start:stop:stop]
+	return portion
+}
+
+// All returns all the temperature readings
+func All() []int {
+	return temps
+}

16-slices/exercises/23-limit-the-backing-array-sharing/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"
+
+	"github.com/inancgumus/learngo/16-slices/exercises/23-limit-the-backing-array-sharing/solution/api"
+)
+
+func main() {
+	temps := api.Read(0, 3)
+	temps = append(temps, []int{1, 3}...)
+
+	fmt.Println("API's readings:", api.All())
+	fmt.Println("Your readings :", temps)
+}