by unix.sh:

The follow is from GO programming lanugage spec:

//spec starts

Type declarations
...
// A Mutex is a data type with two methods Lock and Unlock.
type Mutex struct         { /* Mutex fields */ }
func (m *Mutex) Lock()    { /* Lock implementation */ }
func (m *Mutex) Unlock()  { /* Unlock implementation */ }

// NewMutex has the same composition as Mutex but its method set is empty.
type NewMutex Mutex

// PrintableMutex's method set contains the methods
// Lock and Unlock bound to its anonymous field Mutex.
type PrintableMutex struct {
        Mutex
}

//spec ends

I think the method set in anonymous field Mutex of PrintableMutex doesn't
have two methods: Lock and Unlock, only *Mutex does(the receiver is of *T).
So the comments of PrintableMutex are wrong. It should be *Mutex instead.