raft/raft.go
func (r *raft) promotable() bool {
	_, ok := r.prs[r.id]
	return ok
}
func (r *raft) promotable() bool {
	_, ok := r.prs[r.id]
	return ok
}
func ( r * raft ) promotable ( ) bool { _ , ok := r . prs [ r . id ] return ok }
// promotable indicates whether state machine can be promoted to leader,
// which is true when its own id is in progress list.
promotable indicates whether state machine can be promoted to leader which is true when its own id is in progress list .