Determining unique values in a slice or array in Go requires the use of a map.

unique-list.go

package main

import (
"fmt"
)

func appendUnique(list []string) []string {
	// initialize a map of string keys and boolean values for 
	// keeping track of list entries we've seen.
	uniqueKeys := make(map[string]bool)
	// create an empty slice to hold our unique values.
	uniqueList := []string{}
	
	// Loop over the items in the list. 
	// Underscores are for discarding the index, in the case
	// of the list, and keys, in the case of the map, as we
	// don't need them to determine unique list entries.
	for _, entry := range list {
		// Check the map to see if it has our list entry.
		// If not, the value will be false, and we should
		// add it to the map and set it to true.
		if _, value := uniqueKeys[entry]; !value {
			uniqueKeys[entry] = true
			uniqueList = append(uniqueList, entry)
		}
	}
	
	// Return the list of unique values.
	return uniqueList
}

func main() {
	dupeList := []string{"hello", "hello", "world"}
	dedupedList := appendUnique(dupeList)
	// Starting list
	fmt.Println(dupeList)
	// Ending list
	fmt.Println(dedupedList)
}