code: func (m *Map) Range(f func(key, value interface{}) bool) {
  	for k, v := range m.m {
  		if !f(k, v) {
  			break
  		}
  	}
  }
docs: // Range calls f sequentially for each key and value present in the map.
  // If f returns false, range stops the iteration.
  //
  // Range does not necessarily correspond to any consistent snapshot of the Map's
  // contents: no key will be visited more than once, but if the value for any key
  // is stored or deleted concurrently, Range may reflect any mapping for that key
  // from any point during the Range call.
  //
  // Range may be O(N) with the number of elements in the map even if f returns
  // false after a constant number of calls.