go/src/cmd/internal/bio/must.go

// MustClose closes Closer c and calls log.Fatal if it returns a non-nil error.
func MustClose(c io.Closer) { … }

// MustWriter returns a Writer that wraps the provided Writer,
// except that it calls log.Fatal instead of returning a non-nil error.
func MustWriter(w io.Writer) io.Writer { … }

type mustWriter …

func (w mustWriter) Write(b []byte) (int, error) { … }

func (w mustWriter) WriteString(s string) (int, error) { … }