Comparator

Some data structures (e.g. TreeMap, TreeSet) require a comparator function to automatically keep their elements sorted upon insertion. This comparator is necessary during the initalization.

Comparator is defined as:

Return values (int):

negative , if a < b
zero     , if a == b
positive , if a > b

Comparator signature:

type Comparator func(a, b interface{}) int

All common comparators for builtin types are included in the library:

func StringComparator(a, b interface{}) int
func IntComparator(a, b interface{}) int
func Int8Comparator(a, b interface{}) int
func Int16Comparator(a, b interface{}) int
func Int32Comparator(a, b interface{}) int
func Int64Comparator(a, b interface{}) int
func UIntComparator(a, b interface{}) int
func UInt8Comparator(a, b interface{}) int
func UInt16Comparator(a, b interface{}) int
func UInt32Comparator(a, b interface{}) int
func UInt64Comparator(a, b interface{}) int
func Float32Comparator(a, b interface{}) int
func Float64Comparator(a, b interface{}) int
func ByteComparator(a, b interface{}) int
func RuneComparator(a, b interface{}) int
func TimeComparator(a, b interface{}) int

Writing custom comparators is easy:

package main
import (
    "fmt"
    "github.com/emirpasic/gods/sets/treeset"
)
type User struct {
    id   int
    name string
}
// Custom comparator (sort by IDs)
func byID(a, b interface{}) int {
    // Type assertion, program will panic if this is not respected
    c1 := a.(User)
    c2 := b.(User)
    switch {
    case c1.id > c2.id:
        return 1
    case c1.id < c2.id:
        return -1
    default:
        return 0
    }
}
func main() {
    set := treeset.NewWith(byID)
    set.Add(User{2, "Second"})
    set.Add(User{3, "Third"})
    set.Add(User{1, "First"})
    set.Add(User{4, "Fourth"})
    fmt.Println(set) // {1 First}, {2 Second}, {3 Third}, {4 Fourth}
}