proposal: spec: add built-in set data structure

[gopherbot]

by webuser1200:

When working with large diverse data sets in go I wish I had a built in set data
structure. For now, I've made by using map but my code would be cleaner and simpler if
there was a built in set method.

[cznic]

Comment 1:

IMHO, using a map as a set seems easy enough.

[gopherbot]

Comment 2 by deckarep:

I would love to see a built-in Set in Go as well.  I would argue that a Set is probably
more of a fundamental data structure than even a map.  While we can use a map to model
as a set as I've done here: https://github.com/deckarep/golang-set. I'm still not quite
happy with having to use interface{}.  Also, it's not exactly trivial to come up with a
full implementation that utilizes all the set operations.
Please consider it.

[ianlancetaylor]

Comment 3:

Labels changed: added release-none, repo-main, languagechange.

[davecheney]

Comment 4:

Status changed to Thinking.

[pciet]

https://blog.golang.org/profiling-go-programs shows that slices can be a more efficient representation of an unordered set. In my programming with map[type]struct{} I've used these:

add(set, item) set

combine(sets…) set

reduce(set) set

has(set, item) bool

equal(sets…) bool

diff(setA, setB) set

len(set) int

set.String() string

for item, _ := range set