add: slice internals backing array and slice header
This commit is contained in:
Inanc Gumus
60
16-slices/exercises/16-internals-backing-array-fix/main.go
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60
16-slices/exercises/16-internals-backing-array-fix/main.go
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// For more tutorials: https://blog.learngoprogramming.com
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//
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// Copyright © 2018 Inanc Gumus
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// Learn Go Programming Course
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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//
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package main
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import (
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"fmt"
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"math/rand"
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"time"
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)
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// ---------------------------------------------------------
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// EXERCISE: Fix the backing array problem
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//
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// You receive numbers from an API. After you're done working
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// with it, the API needs to continue using those numbers.
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//
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// But your program changes the numbers (changes the API's slice).
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//
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// Fix the program so that your program doesn't modify
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// the original numbers.
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//
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//
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// RESTRICTION
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//
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// Fix your problem only in the designated area of the code below.
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//
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//
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// EXPECTED OUTPUT
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//
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// Mine : [-50 -100 -150]
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// Original nums: [56 89 15]
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//
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// Note: Original nums may vary (they're random)
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// But your slice should look like the above (mine slice)
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//
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// Yes, it should output only three numbers for the both slices!
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//
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// ---------------------------------------------------------
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func main() {
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// API returns random numbers in an int slice
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rand.Seed(time.Now().UnixNano())
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nums := rand.Perm(100)
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// ----------------------------------------
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// RESTRICTIONS — ONLY ADD YOUR CODE HERE
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//
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mine := nums
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//
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// ----------------------------------------
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mine[0], mine[1], mine[2] = -50, -100, -150
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fmt.Println("Mine :", mine)
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fmt.Println("Original nums:", nums[:3])
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}
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@ -0,0 +1,35 @@
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// For more tutorials: https://blog.learngoprogramming.com
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//
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// Copyright © 2018 Inanc Gumus
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// Learn Go Programming Course
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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//
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package main
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import (
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"fmt"
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"math/rand"
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"time"
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)
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func main() {
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rand.Seed(time.Now().UnixNano())
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nums := rand.Perm(100)
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// ----------------------------------------
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// breaks the connection:
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// mine and nums now have different backing arrays
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// verbose solution:
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// var mine []int
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// mine = append(mine, nums[:3]...)
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// better solution (almost the same thing):
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mine := append([]int(nil), nums[:3]...)
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// ----------------------------------------
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mine[0], mine[1], mine[2] = -50, -100, -150
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fmt.Println("Mine :", mine)
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fmt.Println("Original nums:", nums[:3])
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}
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52
16-slices/exercises/17-internals-backing-array-sort/main.go
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52
16-slices/exercises/17-internals-backing-array-sort/main.go
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// For more tutorials: https://blog.learngoprogramming.com
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//
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// Copyright © 2018 Inanc Gumus
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// Learn Go Programming Course
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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//
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package main
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import (
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"fmt"
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)
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// ---------------------------------------------------------
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// EXERCISE: Sort the backing array
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//
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// 1. Sort only the middle 3 items.
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//
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// 2. All the slices should see your change.
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//
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//
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// RESTRICTION
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//
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// Do not sort manually. Sort by slicing then by using the sort package.
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//
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//
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// EXPECTED OUTPUT
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//
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// Original: [pacman mario tetris doom galaga frogger asteroids simcity metroid defender rayman tempest ultima]
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//
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// Sorted : [pacman mario tetris doom galaga asteroids frogger simcity metroid defender rayman tempest ultima]
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//
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//
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// HINT:
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//
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// Middle items are : [frogger asteroids simcity]
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//
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// After sorting they become: [asteroids frogger simcity]
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//
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// ---------------------------------------------------------
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func main() {
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items := []string{
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"pacman", "mario", "tetris", "doom", "galaga", "frogger",
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"asteroids", "simcity", "metroid", "defender", "rayman",
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"tempest", "ultima",
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}
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fmt.Println("Original:", items)
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fmt.Println()
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fmt.Println("Sorted :", items)
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}
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@ -0,0 +1,33 @@
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// For more tutorials: https://blog.learngoprogramming.com
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//
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// Copyright © 2018 Inanc Gumus
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// Learn Go Programming Course
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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//
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package main
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import (
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"fmt"
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"sort"
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)
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func main() {
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items := []string{
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"pacman", "mario", "tetris", "doom", "galaga", "frogger",
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"asteroids", "simcity", "metroid", "defender", "rayman",
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"tempest", "ultima",
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}
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fmt.Println("Original:", items)
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mid := len(items) / 2
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smid := items[mid-1 : mid+2]
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// sorting the smid will affect the items
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// as well. their backing array is the same.
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sort.Strings(smid)
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fmt.Println()
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fmt.Println("Sorted :", items)
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}
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115
16-slices/exercises/18-internals-slice-header/main.go
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115
16-slices/exercises/18-internals-slice-header/main.go
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package main
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import (
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"fmt"
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"runtime"
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"runtime/debug"
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)
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// ---------------------------------------------------------
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// EXERCISE: Observe the memory allocations
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//
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// In this exercise, your goal is to observe the memory allocation
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// differences between arrays and slices.
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//
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// You will create, assign arrays and slices then you will print
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// the memory usage of your program on each step.
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//
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// Please follow the instructions inside the code.
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//
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//
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// EXPECTED OUTPUT
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//
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// Note that, your memory usage numbers may vary. These are on my
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// own system. However, the size of the arrays and slices should be
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// the same on your own system as well (if you're on 64-bit machine).
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//
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//
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// <<< initial memory usage >>>
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// > Memory Usage: 104 KB
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// <<< after declaring an array >>>
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// > Memory Usage: 78235 KB
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// <<< after copying the array >>>
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// > Memory Usage: 156365 KB
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// <<< inside passArray >>>
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// > Memory Usage: 234495 KB
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// <<< after slicings >>>
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// > Memory Usage: 234497 KB
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// <<< inside passSlice >>>
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// > Memory Usage: 234497 KB
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//
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// Array's size : 80000000 bytes.
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// Array2's size: 80000000 bytes.
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// Slice1's size: 24 bytes.
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// Slice2's size: 24 bytes.
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// Slice3's size: 24 bytes.
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//
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//
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// HINTS
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//
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// I've declared a few function to help you.
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//
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// report function prints the memory usage.
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// Just call it with a message that matches to the expected output.
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//
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// passArray function accepts a [size]int array, so you can pass it
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// your array. It automatically prints the memory usage.
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//
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// passSlice function accepts an int slice, so you can pass it
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// your one of your slices. It automatically prints the memory usage.
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//
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// ---------------------------------------------------------
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const size = 1e7
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func main() {
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// stops the gc: prevents cleaning up the memory
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debug.SetGCPercent(-1)
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// run the program to see what this prints
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report("initial memory usage")
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// 1. allocate an array with 10 million int elements
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// this array's size is equal to ~80MB
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// hint: use the `size` constant
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//
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// 2. print the memory usage
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// 3. copy the array to a new array (just assign)
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// 4. print the memory usage
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// 5. pass the array to passArray function
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// 6. convert the array to a slice (by slicing)
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// 7. slice only the first 1000 elements of the array
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// 8. slice only the elements of the array between 1000 and 10000
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// 9. print the memory usage
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// 10. pass the one of the slices to passSlice function
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// 11. print the sizes of the arrays and slices
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// hint: use the unsafe.Sizeof function
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}
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// observe that passing an array affects the memory usage dramatically
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//
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// passes [size]int array — about 80MB!
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func passArray(items [size]int) {
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items[0] = 100
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report("inside passArray")
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}
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// observe that passing a slice doesn't affect the memory usage
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//
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// only passes 24-bytes of slice header
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func passSlice(items []int) {
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items[0] = 100
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report("inside passSlice")
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}
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func report(msg string) {
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var m runtime.MemStats
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runtime.ReadMemStats(&m)
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fmt.Printf("<<< %s >>>\n", msg)
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fmt.Printf("\t> Memory Usage: %v KB\n", m.Alloc/1024)
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}
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@ -0,0 +1,62 @@
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// For more tutorials: https://blog.learngoprogramming.com
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//
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// Copyright © 2018 Inanc Gumus
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// Learn Go Programming Course
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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//
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package main
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import (
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"fmt"
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"runtime"
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"runtime/debug"
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"unsafe"
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)
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const size = 1e7
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func main() {
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// stops the gc: prevents cleaning up the memory
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debug.SetGCPercent(-1)
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report("initial memory usage")
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var array [size]int
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report("after declaring an array")
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array2 := array
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report("after copying the array")
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passArray(array)
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slice1 := array[:]
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slice2 := array[1e3:]
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slice3 := array[1e3:1e4]
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report("after slicings")
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passSlice(slice3)
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fmt.Println()
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fmt.Printf("Array's size : %d bytes.\n", unsafe.Sizeof(array))
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fmt.Printf("Array2's size: %d bytes.\n", unsafe.Sizeof(array2))
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fmt.Printf("Slice1's size: %d bytes.\n", unsafe.Sizeof(slice1))
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fmt.Printf("Slice2's size: %d bytes.\n", unsafe.Sizeof(slice2))
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fmt.Printf("Slice3's size: %d bytes.\n", unsafe.Sizeof(slice3))
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}
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func passArray(items [size]int) {
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items[0] = 100
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report("inside passArray")
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}
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func passSlice(items []int) {
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report("inside passSlice")
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}
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func report(msg string) {
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var m runtime.MemStats
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runtime.ReadMemStats(&m)
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fmt.Printf("<<< %s >>>\n", msg)
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fmt.Printf("\t> Memory Usage: %v KB\n", m.Alloc/1024)
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}
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@ -41,4 +41,14 @@ These are warm-up exercises that will reinforce your knowledge of slices.
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2. **[Slicing by arguments](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/14-slicing-by-args)**
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3. **[Slicing the Housing Prices](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/15-slicing-housing-prices)**
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3. **[Slicing the Housing Prices](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/15-slicing-housing-prices)**
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---
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## Exercises Level IV - Internals
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1. **[Fix the backing array problems](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/16-internals-backing-array-fix)**
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2. **[Sort the backing array](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/17-internals-backing-array-sort)**
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3. **[Observe the memory allocations](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/18-internals-slice-header)**
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