feat: reverse echo

.gitignore

@@ -6,6 +6,7 @@
 *.dylib
 cmd/diagnosis/diagnosis
 cmd/diagnosis/diagnosis.*
+cmd/echor/echor
 
 # Test binary, build with `go test -c`
 *.test

cmd/echor/main.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/wangyoucao577/go-project-layout/stringutil"
+)
+
+func main() {
+	if len(os.Args) > 1 {
+		fmt.Println(stringutil.Reverse(os.Args[1]))
+	} else {
+		fmt.Println() // print empty string
+	}
+}

stringutil/reverse.go

@@ -0,0 +1,11 @@
+// Package stringutil contains utility functions for working with strings.
+package stringutil
+
+// Reverse returns its argument string reversed rune-wise left to right.
+func Reverse(s string) string {
+	r := []rune(s)
+	for i, j := 0, len(r)-1; i < len(r)/2; i, j = i+1, j-1 {
+		r[i], r[j] = r[j], r[i]
+	}
+	return string(r)
+}

stringutil/reverse_test.go

@@ -0,0 +1,20 @@
+package stringutil
+
+import "testing"
+
+func TestReverse(t *testing.T) {
+	cases := []struct {
+		in, want string
+	}{
+		{"Hello, world", "dlrow ,olleH"},
+		{"Hello, 世界", "界世 ,olleH"},
+		{"", ""},
+	}
+
+	for _, c := range cases {
+		got := Reverse(c.in)
+		if got != c.want {
+			t.Errorf("Reverse(%q) == %q, want %q", c.in, got, c.want)
+		}
+	}
+}