ergo/vendor/github.com/tidwall/btree/README.md

BTree implementation for Go

This package provides an in-memory B-Tree implementation for Go, useful as an ordered, mutable data structure.

This is a fork of the wonderful google/btree package. It’s has all the same great features and adds a few more.

• Descend* functions for iterating backwards.
• Iteration performance boost.
• User defined context.

User defined context

This is a great new feature that allows for entering the same item into multiple B-trees, and each B-tree have a different ordering formula.

For example:

package main

import (
    "fmt"

    "github.com/tidwall/btree"
)

type Item struct {
    Key, Val string
}

func (i1 *Item) Less(item btree.Item, ctx interface{}) bool {
    i2 := item.(*Item)
    switch tag := ctx.(type) {
    case string:
        if tag == "vals" {
            if i1.Val < i2.Val {
                return true
            } else if i1.Val > i2.Val {
                return false
            }
            // Both vals are equal so we should fall though
            // and let the key comparison take over.
        }
    }
    return i1.Key < i2.Key
}

func main() {

    // Create a tree for keys and a tree for values.
    // The "keys" tree will be sorted on the Keys field.
    // The "values" tree will be sorted on the Values field.
    keys := btree.New(16, "keys")
    vals := btree.New(16, "vals")

    // Create some items.
    users := []*Item{
        &Item{Key: "user:1", Val: "Jane"},
        &Item{Key: "user:2", Val: "Andy"},
        &Item{Key: "user:3", Val: "Steve"},
        &Item{Key: "user:4", Val: "Andrea"},
        &Item{Key: "user:5", Val: "Janet"},
        &Item{Key: "user:6", Val: "Andy"},
    }

    // Insert each user into both trees
    for _, user := range users {
        keys.ReplaceOrInsert(user)
        vals.ReplaceOrInsert(user)
    }

    // Iterate over each user in the key tree
    keys.Ascend(func(item btree.Item) bool {
        kvi := item.(*Item)
        fmt.Printf("%s %s\n", kvi.Key, kvi.Val)
        return true
    })

    fmt.Printf("\n")
    // Iterate over each user in the val tree
    vals.Ascend(func(item btree.Item) bool {
        kvi := item.(*Item)
        fmt.Printf("%s %s\n", kvi.Key, kvi.Val)
        return true
    })
}

// Should see the results
/*
user:1 Jane
user:2 Andy
user:3 Steve
user:4 Andrea
user:5 Janet
user:6 Andy

user:4 Andrea
user:2 Andy
user:6 Andy
user:1 Jane
user:3 Steve
*/