func之后的括号在Go中意味着什么？

As a Go beginner, I stumbled across code where there are brackets directly after func

func (v Version) MarshalJSON() ([]byte, error) {
  return json.Marshal(v.String())
}

So what does (v Version) mean?

This is not a function but a method. In this case, it adds the MarshalJSON method to the Version struct type.

The v is the name for the received value (and would be analogous to this in a Java method or self in Python), the Version specifies the type we're adding the method to.

See go by example for, well, an example, and the specification for more details.