Implementing a set using a map

A set is useful to remove duplicates from a collection of values. Maps can be used as sets efficiently by utilizing a zero-size value structure.

How to do it...

Use a map whose key type is the element type of the set, and whose value type is struct{}:

stringSet := make(map[string]struct{})

Add values to the set with the struct{}{} value:

stringSet[value]=struct{}{}

Check for value existence using the two-value version of map lookup:

if _,exists:=stringSet[str]; exists {
  // String str exists in the set
}

A map is not ordered. If the ordering of elements is important, keep a slice with the map:

// Remove duplicate inputs from the input, preserving order
func DedupOrdered(input []string) []string {
   set:=make(map[string]struct{})
   output:=make([]string,0,len(input))
   for _,in:=range input {
     if _,exists:=set[in]; exists {
   ...