go - What does a function without body mean?

Question

I'm reading the code that package time, and then I want to know how the func After(d Duration) <-chan Time works.

I found the code follows:

func After(d Duration) <-chan Time {
    return NewTimer(d).C
}

func NewTimer(d Duration) *Timer {
    c := make(chan Time, 1)
    t := &Timer{
        C: c,
        r: runtimeTimer{
            when: nano() + int64(d),
            f:    sendTime,
            arg:  c,
        },
    }
    startTimer(&t.r)
    return t
}

So I found the definition of startTimer - it's so weird that function startTimer does not have a function body.

func startTimer(*runtimeTimer)

I want to know that :

1. Where is the real code of startTimer
2. Why an "abstract method" can exists here
3. Why the author of Go wrote it like this

Thanks!

Answer 1

Waitting for answers