fixed-size set in Go

idcache.go

type idCache struct {
    data    map[string]*string
    maxSize int
    newest  *string
    oldest  *string
}

func newIdCache(size int) *idCache {
    return &idCache{
        data:    make(map[string]*string, size),
        maxSize: size,
        newest:  nil,
        oldest:  nil,
    }
}

func (c *idCache) has(s string) bool {
    _, haz := c.data[s]
    return haz
}

func (c *idCache)add(s string) {
    if c.newest != nil {
        c.data[*c.newest] = &s
    }
    c.newest = &s

    if c.oldest == nil {
        c.oldest = &s
    }

    for len(c.data) >= c.maxSize {
        o := *c.oldest
        c.oldest = c.data[o]
        delete(c.data, o)
    }

    c.data[s] = nil
}

note: this isn't threadsafe. You'll need to toss in a sync.RWMutex to make it threadsafe. In my application, the things I'm de-duping come off a channel so they're already seriealized so I don't bother.

ugh, serialized, that is.