update book code

eBook/examples/chapter_10/struct_conversions.go

@@ -0,0 +1,24 @@
+// struct_conversions.go
+package main
+
+import (
+	"fmt"
+)
+
+type number struct {
+	f	float32
+}
+
+type nr number   // alias type
+
+func main() {
+	a := number{5.0}
+	b := nr{5.0}
+	// var i float32 = b   // compile-error: cannot use b (type nr) as type float32 in assignment
+	// var i = float32(b)  // compile-error: cannot convert b (type nr) to type float32
+	// var c number = b    // compile-error: cannot use b (type nr) as type number in assignment
+	// needs a conversion:
+	var c = number(b)
+	fmt.Println(a, b, c)
+}
+// output: {5} {5} {5}