Errata

Creating a Multishape like described: multiShape := MultiShape { shapes : [] Shape { Circle { 0 , 0 , 5 }, Rectangle { 0 , 0 , 10 , 10 }, }, } spits a compile error: cannot use Circle literal (type Circle) as type Shape in array or slice literal: Circle does not implement Shape (area method has pointer receiver) cannot use Rectangle literal (type Rectangle) as type Shape in array or slice literal: Rectangle does not implement Shape (area method has pointer receiver)

Note from the Author or Editor:
Apologies, the area method for Circle and Rectangle should be non-pointer types: func (c Circle) area() float64 { return math.Pi * c.r*c.r } func (r Rectangle) area() float64 { l := distance(r.x1, r.y1, r.x1, r.y2) w := distance(r.x1, r.y1, r.x2, r.y1) return l * w } Or the literals should be constructed like this: multiShape := MultiShape{ shapes: []Shape{ &Circle { 0 , 0 , 5 }, &Rectangle { 0 , 0 , 10 , 10 }, }, }

The import is missing one package: "io" On the next page, page 74, there is a line of code : _, err := io.Copy(h, f) This will get error if there is no "io" package in the import statement. The import should be: import ( "fmt" "hash/crc32" "io/ioutil" "io" )

Note from the Author or Editor:
Yes this is a mistake. "io/ioutil" should be replaced with "io": package main import ( "fmt" "hash/crc32" "io" "os" ) func getHash(filename string) (uint32, error) { // open the file f, err := os.Open(filename) if err != nil { return 0, err } // remember to always close opened files defer f.Close() // create a hasher h := crc32.NewIEEE() // copy the file into the hasher // - copy takes (dst, src) and returns (bytesWritten, error) _, err = io.Copy(h, f) // we don't care about how many bytes were written, but we do want to // handle the error if err != nil { return 0, err } return h.Sum32(), nil } func main() { h1, err := getHash("test1.txt") if err != nil { return } h2, err := getHash("test2.txt") if err != nil { return } fmt.Println(h1, h2, h1 == h2) }

As printed (in the Safari Online Book) the second program listed - the one with the getHash function has *several* compile errors with go version go1.5.3 darwin/amd64. dhassler% go run crc32.go # command-line-arguments ./crc32.go:6: imported and not used: "io/ioutil" ./crc32.go:11: undefined: os in os.Open ./crc32.go:22: no new variables on left side of := ./crc32.go:22: undefined: io in io.Copy I have resolved each to get the example to run but would be interested in the author's solutions - what is the correct version of this example? Have the examples in the book been tested???

Note from the Author or Editor:
The example is indeed broken. A corrected version is here: https://play.golang.org/p/ofZVaifgJG I made the following changes: * The imports are: import ( "fmt" "io" "os" "hash/crc32" ) * Since `err` was already defined I changed `:=` to `=` for: _, err = io.Copy(h, f)