update: directory structure

advfuncs/exercises/01-refactor/main.go

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+package main
+
+import "fmt"
+
+// ---------------------------------------------------------
+// EXERCISE: Refactor
+//
+//   In the headerOf function, instead of using a switch,
+//   use a map. Declare it at the package-level.
+//
+// RESTRICTION
+//
+//   For panicking, use a deferred function and a named param.
+//
+// EXPECTED OUTPUT
+//
+//   Please run the solution.
+//
+// ---------------------------------------------------------
+
+func main() {
+	fmt.Println(headerOf("gif"))
+}
+
+func headerOf(format string) string {
+	switch format {
+	case "png":
+		return "\x89PNG\r\n\x1a\n"
+	case "jpg":
+		return "\xff\xd8\xff"
+	}
+	panic("unknown format: " + format)
+}

advfuncs/exercises/01-refactor/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() {
+	fmt.Println(headerOf("gif"))
+}
+
+var headers = map[string]string{
+	"png": "\x89PNG\r\n\x1a\n",
+	"jpg": "\xff\xd8\xff",
+}
+
+func headerOf(format string) (header string) {
+	defer func() {
+		if header == "" {
+			panic("unknown format: " + format)
+		}
+	}()
+	return headers[format]
+}

advfuncs/exercises/README.md

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+# Header
+
+What you will learn?
+
+1. **[Refactor](https://github.com/inancgumus/learngo/tree/master/28-error-handling/exercises/01-refactor)**
+
+    Refactor the headerOf function with a map + defer + and a named param.
+
+2. **[text](https://github.com/inancgumus/learngo/tree/master/)**
+
+    text