README.md
1gtreap
2------
3
4gtreap is an immutable treap implementation in the Go Language
5
6[](https://godoc.org/github.com/steveyen/gtreap) [](https://drone.io/github.com/steveyen/gtreap/latest) [](https://coveralls.io/r/steveyen/gtreap)
7
8Overview
9========
10
11gtreap implements an immutable treap data structure in golang.
12
13By treap, this data structure is both a heap and a binary search tree.
14
15By immutable, any updates/deletes to a treap will return a new treap
16which can share internal nodes with the previous treap. All nodes in
17this implementation are read-only after their creation. This allows
18concurrent readers to operate safely with concurrent writers as
19modifications only create new data structures and never modify
20existing data structures. This is a simple approach to achieving MVCC
21or multi-version concurrency control.
22
23By heap, items in the treap follow the heap-priority property, where a
24parent node will have higher priority than its left and right children
25nodes.
26
27By binary search tree, items are store lexigraphically, ordered by a
28user-supplied Compare function.
29
30To get a probabilistic O(lg N) tree height, you should use a random
31priority number during the Upsert() operation.
32
33LICENSE
34=======
35
36MIT
37
38Example
39=======
40
41 import (
42 "math/rand"
43 "github.com/steveyen/gtreap"
44 )
45
46 func stringCompare(a, b interface{}) int {
47 return bytes.Compare([]byte(a.(string)), []byte(b.(string)))
48 }
49
50 t := gtreap.NewTreap(stringCompare)
51 t = t.Upsert("hi", rand.Int())
52 t = t.Upsert("hola", rand.Int())
53 t = t.Upsert("bye", rand.Int())
54 t = t.Upsert("adios", rand.Int())
55
56 hi = t.Get("hi")
57 bye = t.Get("bye")
58
59 // Some example Delete()'s...
60 t = t.Delete("bye")
61 nilValueHere = t.Get("bye")
62 t2 = t.Delete("hi")
63 nilValueHere2 = t2.Get("hi")
64
65 // Since we still hold onto treap t, we can still access "hi".
66 hiStillExistsInTreapT = t.Get("hi")
67
68 t.VisitAscend("cya", func(i Item) bool {
69 // This visitor callback will be invoked with every item
70 // from "cya" onwards. So: "hi", "hola".
71 // If we want to stop visiting, return false;
72 // otherwise a true return result means keep visiting items.
73 return true
74 })
75
76Tips
77====
78
79The Upsert() method takes both an Item (an interface{}) and a heap
80priority. Usually, that priority should be a random int
81(math/rand.Int()) or perhaps even a hash of the item. However, if you
82want to shuffle more commonly accessed items nearer to the top of the
83treap for faster access, at the potential cost of not approaching a
84probabilistic O(lg N) tree height, then you might tweak the priority.
85
86See also
87========
88
89For a simple, ordered, key-value storage or persistence library built
90on immutable treaps, see: https://github.com/steveyen/gkvlite
91
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