add: slice internals backing array and slice header

16-slices/exercises/18-internals-slice-header/solution/main.go

@@ -0,0 +1,62 @@
+// 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"
+	"runtime"
+	"runtime/debug"
+	"unsafe"
+)
+
+const size = 1e7
+
+func main() {
+	// stops the gc: prevents cleaning up the memory
+	debug.SetGCPercent(-1)
+
+	report("initial memory usage")
+
+	var array [size]int
+	report("after declaring an array")
+
+	array2 := array
+	report("after copying the array")
+
+	passArray(array)
+
+	slice1 := array[:]
+	slice2 := array[1e3:]
+	slice3 := array[1e3:1e4]
+	report("after slicings")
+
+	passSlice(slice3)
+
+	fmt.Println()
+	fmt.Printf("Array's size : %d bytes.\n", unsafe.Sizeof(array))
+	fmt.Printf("Array2's size: %d bytes.\n", unsafe.Sizeof(array2))
+	fmt.Printf("Slice1's size: %d bytes.\n", unsafe.Sizeof(slice1))
+	fmt.Printf("Slice2's size: %d bytes.\n", unsafe.Sizeof(slice2))
+	fmt.Printf("Slice3's size: %d bytes.\n", unsafe.Sizeof(slice3))
+}
+
+func passArray(items [size]int) {
+	items[0] = 100
+	report("inside passArray")
+}
+
+func passSlice(items []int) {
+	report("inside passSlice")
+}
+
+func report(msg string) {
+	var m runtime.MemStats
+	runtime.ReadMemStats(&m)
+	fmt.Printf("<<< %s >>>\n", msg)
+	fmt.Printf("\t> Memory Usage: %v KB\n", m.Alloc/1024)
+}