Yes, it currently requires two lookups (two hashes, two bucket searches, etc.). This general problem is issue 17133 (https://github.com/golang/go/issues/17133). Your example has the extra complication that the update operation is an append, not just a +=.
On Sunday, November 27, 2016 at 7:00:23 AM UTC-8, Ian Cottrell wrote: > > Yes you will get two map operations happen, one lookup and one assign. > > Wrapping the code into a (mildly modified for pretty output) runnable > example: https://play.golang.org/p/oGKvfS9ssH > > In the basic case of a new key, there is no way to avoid doing both a > lookup and assign, but in the case where the key exists, you can avoid the > assign by adding another level of indirection, like this: > https://play.golang.org/p/Rsm1uT4tlP > You can see the only changes are the type of the likes map (from > map[string]People to map[string]*People), and the way it's modified in the > loop. > I don't recommend actually doing this in general though. The result is not > horrific, but it's definitely less clear, and most cases where the map > lookup is actually a significant factor, you have probably already picked > the wrong algorithm, so micro optimising it is not going to get you far. At > the very least you would want to see it actually improve a benchmark before > going with it. > > > On Sun, 27 Nov 2016 at 13:40 <stinkin...@gmail.com <javascript:>> wrote: > >> I should clarify that this actually came up in practice and I have no >> clue on how I can eliminate them >> >> -- >> You received this message because you are subscribed to the Google Groups >> "golang-nuts" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to golang-nuts...@googlegroups.com <javascript:>. >> For more options, visit https://groups.google.com/d/optout. >> > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
