Explain this code

In Go there are various ways to return a struct value or slice thereof. Could you explain the difference?

type MyStruct struct {
    Val int
}

func myfunc() MyStruct {
    return MyStruct{Val: 1}
}

func myfunc() *MyStruct {
    return &MyStruct{}
}

func myfunc(s *MyStruct) {
    s.Val = 1
}

Shortly:

• the first returns a copy of the struct,
• the second a pointer to the struct value created within the function,
• the third expects an existing struct to be passed in and overrides the value.