add: slice internals exercises

16-slices/exercises/19-observe-len-cap/main.go

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+package main
+
+import "fmt"
+
+// ---------------------------------------------------------
+// EXERCISE: Observe the length and capacity
+//
+//  Follow the instructions inside the code below to
+//  gain more intuition about the length and capacity of a slice.
+//
+// ---------------------------------------------------------
+
+func main() {
+	// --- #1 ---
+	// 1. create a new slice named: games
+	//
+	// 2. print the length and capacity of the games slice
+	//
+	// 3. comment out the games slice
+	//    then declare it as an empty slice
+	//
+	// 4. print the length and capacity of the games slice
+	//
+	// 5. append the elements: "pacman", "mario", "tetris", "doom"
+	//
+	// 6. print the length and capacity of the games slice
+	//
+	// 7. comment out everything
+	//
+	// 8. declare it again using a slice literal
+	//    (use the same elements from step 3)
+
+	// --- #2 ---
+	// 1. use a loop from 0 to 4 to slice the games slice, element by element.
+	//
+	// 2. print its length and capacity along the way (in the loop).
+
+	fmt.Println()
+	// for ... {
+	// 	fmt.Printf("games[:%d]'s len: %d cap: %d\n", ...)
+	// }
+
+	// --- #3 ---
+	// 1. slice the games slice up to zero element
+	//    (save the result to a new slice named: "zero")
+	//
+	// 2. print the games and the new slice's len and cap
+	//
+	// 3. append a new element to the new slice
+	//
+	// 4. print the new slice's lens and caps
+	//
+	// 5. repeat the last two steps 5 times (use a loop)
+	//
+	// 6. notice the growth of the capacity after the 5th append
+	//
+	// Use this slice's elements to append to the new slice:
+	// []string{"ultima", "dagger", "pong", "coldspot", "zetra"}
+	fmt.Println()
+
+	// zero := ...
+	// fmt.Printf("games's     len: %d cap: %d\n", ...)
+	// fmt.Printf("zero's      len: %d cap: %d\n", ...)
+
+	// for ... {
+	//   ...
+	//   fmt.Printf("zero's      len: %d cap: %d\n", ...)
+	// }
+
+	// --- #4 ---
+	// using a range loop, slice the zero slice element by element,
+	// and print its length and capacity along the way.
+	//
+	// observe that, the range loop only loops for the length, not the cap.
+	fmt.Println()
+
+	// for ... {
+	//   s := zero[:n]
+	//   fmt.Printf("zero[:%d]'s  len: %d cap: %d\n", ...)
+	// }
+
+	// --- #5 ---
+	// 1. do the 3rd step above again but this time, start by slicing
+	//    the zero slice up to its capacity (use the cap function).
+	//
+	// 2. print the elements of the zero slice in the loop.
+	fmt.Println()
+
+	// zero = ...
+	// for ... {
+	//   fmt.Printf("zero[:%d]'s  len: %d cap: %d - %q\n", ...)
+	// }
+
+	// --- #6 ---
+	// 1. change the one of the elements of the zero slice
+	//
+	// 2. change the same element of the games slice
+	//
+	// 3. print the games and the zero slices
+	//
+	// 4. observe that they don't have the same backing array
+	fmt.Println()
+	// ...
+	// fmt.Printf("zero  : %q\n", zero)
+	// fmt.Printf("games : %q\n", games)
+
+	// --- #7 ---
+	// try to slice the games slice beyond its capacity
+}

16-slices/exercises/19-observe-len-cap/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"
+
+func main() {
+	// --- #1 ---
+	// var games []string
+	// fmt.Printf("games's len    : %d cap: %d\n", len(games), cap(games))
+
+	// games := []string{}
+	// fmt.Printf("games's len    : %d cap: %d\n", len(games), cap(games))
+
+	// games = append(games, "pacman", "mario", "tetris", "doom")
+	// fmt.Printf("games's len    : %d cap: %d\n", len(games), cap(games))
+
+	games := []string{"pacman", "mario", "tetris", "doom"}
+	fmt.Printf("games's len    : %d cap: %d\n", len(games), cap(games))
+
+	// --- #2 ---
+	fmt.Println()
+
+	for i := 0; i <= len(games); i++ {
+		s := games[:i]
+		fmt.Printf("games[:%d]'s len: %d cap: %d\n", i, len(s), cap(s))
+	}
+
+	// --- #3 ---
+	fmt.Println()
+
+	zero := games[:0]
+	fmt.Printf("games's     len: %d cap: %d\n", len(games), cap(games))
+	fmt.Printf("zero's      len: %d cap: %d\n", len(zero), cap(zero))
+
+	for _, v := range []string{"ultima", "dagger", "pong", "coldspot", "zetra"} {
+		zero = append(zero, v)
+		fmt.Printf("zero's      len: %d cap: %d\n", len(zero), cap(zero))
+	}
+
+	// --- #4 ---
+	fmt.Println()
+
+	for n := range zero {
+		s := zero[:n]
+		fmt.Printf("zero[:%d]'s  len: %d cap: %d\n", n, len(s), cap(s))
+	}
+
+	// --- #5 ---
+	fmt.Println()
+
+	zero = zero[:cap(zero)]
+	for n := range zero {
+		s := zero[:n]
+		fmt.Printf("zero[:%d]'s  len: %d cap: %d - %q\n", n, len(s), cap(s), s)
+	}
+
+	// --- #6 ---
+	fmt.Println()
+
+	zero[0] = "command & conquer"
+	games[0] = "red alert"
+	fmt.Printf("zero  : %q\n", zero)
+	fmt.Printf("games : %q\n", games)
+
+	// --- #7 ---
+	// uncomment and see the error.
+	// _ = games[:cap(games)+1]
+	// or:
+	// _ = games[:5]
+}