const scheme … type passthroughBuilder … func (*passthroughBuilder) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOptions) (resolver.Resolver, error) { … } func (*passthroughBuilder) Scheme() string { … } type passthroughResolver … func (r *passthroughResolver) start() { … } func (*passthroughResolver) ResolveNow(o resolver.ResolveNowOptions) { … } func (*passthroughResolver) Close() { … } func init() { … }