add: slice internals last lectures

16-slices/10-slice-internals-3-len-cap/1-theory/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"
+
+	s "github.com/inancgumus/prettyslice"
+)
+
+func main() {
+	s.MaxPerLine = 6
+	s.PrintBacking = true
+
+	ages := []int{35, 15, 25}
+	s.Show("ages", ages)
+
+	s.Show("ages[0:0]", ages[0:0])
+
+	for i := 1; i < 4; i++ {
+		txt := fmt.Sprintf("ages[%d:%d]", 0, i)
+		s.Show(txt, ages[0:i])
+	}
+
+	s.Show("append", append(ages, 50))
+}

16-slices/10-slice-internals-3-len-cap/2-example/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 (
+	s "github.com/inancgumus/prettyslice"
+)
+
+func main() {
+	s.PrintBacking = true
+
+	// ----------------------------------------------------
+	// #1 nil slice
+	var games []string // nil slice
+	s.Show("games", games)
+
+	// ----------------------------------------------------
+	// #2 empty slice
+	games = []string{} // empty slice
+	s.Show("games", games)
+	// s.Show("another empty", []int{})
+
+	// ----------------------------------------------------
+	// #3 non-empty slice
+	games = []string{"pacman", "mario", "tetris", "doom"}
+	s.Show("games", games)
+
+	// ----------------------------------------------------
+	// #4 reset the part using the games slice
+	//    part is empty but its cap is still 4
+	part := games
+	s.Show("part", part)
+
+	part = games[:0]
+	s.Show("part[:0]", part)
+	s.Show("part[:cap]", part[:cap(part)])
+
+	for cap(part) != 0 {
+		part = part[1:cap(part)]
+		s.Show("part", part)
+	}
+
+	// #6 backing array's elements become inaccessible
+	// games = games[len(games):]
+
+	// ----------------------------------------------------
+	// #5 part doesn't have any more capacity
+	//    games slice is still intact
+	s.Show("part", part)
+	s.Show("games", games)
+}

16-slices/11-slice-internals-4-append/1-theory/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 (
+	s "github.com/inancgumus/prettyslice"
+)
+
+func main() {
+	s.PrintBacking = true
+
+	ages := []int{35, 15}
+	s.Show("ages", ages)
+
+	ages = append(ages, 5)
+	s.Show("append(ages, 5)", ages)
+}

16-slices/11-slice-internals-4-append/2-example/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 (
+	s "github.com/inancgumus/prettyslice"
+)
+
+func main() {
+	s.PrintBacking = true
+
+	// #1: a nil slice has no backing array
+	var nums []int
+	s.Show("no backing array", nums)
+
+	// #2: creates a new backing array
+	nums = append(nums, 1, 3)
+	s.Show("allocates", nums)
+
+	// #3: creates a new backing array
+	nums = append(nums, 2)
+	s.Show("free capacity", nums)
+
+	// #4: uses the same backing array
+	nums = append(nums, 4)
+	s.Show("no allocation", nums)
+
+	// GOAL: append new odd numbers in the middle
+	// [1 3 2 4] -> [1 3 7 9 2 4]
+
+	// #6: [1 3 2 4] -> [1 3 2 4 2 4]
+	nums = append(nums, nums[2:]...)
+	s.Show("nums <- nums[2:]", nums)
+
+	// #5: overwrites: [1 3 2 4 2 4] -> [1 3 7 9]
+	nums = append(nums[:2], 7, 9)
+	s.Show("nums[:2] <- 7, 9", nums)
+
+	// #7: [1 3 7 9] -> [1 3 7 9 2 4]
+	nums = nums[:6]
+	s.Show("nums: extend", nums)
+}
+
+// don't mind about these options
+// they're just for printing the slices nicely
+func init() {
+	s.MaxPerLine = 10
+	s.Width = 45
+}

16-slices/11-slice-internals-4-append/3-example-growth/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 (
+	"math/rand"
+	"time"
+
+	s "github.com/inancgumus/prettyslice"
+	"github.com/inancgumus/screen"
+)
+
+func main() {
+	s.PrintBacking = true
+	s.MaxPerLine = 30
+	s.Width = 150
+
+	var nums []int
+
+	screen.Clear()
+	for cap(nums) <= 128 {
+		screen.MoveTopLeft()
+
+		s.Show("nums", nums)
+		nums = append(nums, rand.Intn(9)+1)
+
+		time.Sleep(time.Second / 4)
+	}
+}

16-slices/11-slice-internals-4-append/4-example-growth/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"
+)
+
+func main() {
+	ages, oldCap := []int{1}, 1.
+
+	for len(ages) < 5e5 {
+		ages = append(ages, 1)
+
+		c := float64(cap(ages))
+		if c != oldCap {
+			fmt.Printf("len:%-10d cap:%-10g growth:%.2f\n",
+				len(ages), c, c/oldCap)
+		}
+		oldCap = c
+	}
+}