String interning in Golang

intern.go

package intern

import (
  "sync"
)

type Pool struct {
  sync.RWMutex
  lookup map[string]string
}

func New() *Pool {
  return &Pool{lookup: make(map[string]string)}
}

func (p *Pool) Intern(s string) string {
  p.RLock()
  ss, exists := p.lookup[s]
  p.RUnlock()
  if exists { return ss }

  p.Lock()
  defer p.Unlock()
  ss, exists = p.lookup[s]
  if exists { return ss }
  p.lookup[s] = s
  return s
}