How do you implement a set data structure in Go?
Jul 31, 2025 am 09:41 AM
Go does not have built-in collection types, but it can achieve efficient and type-safe collections through map[T]struct{}. 1. Use map[T]struct{} to implement type-safe collections: define a generic Set structure and provide Add, Remove, Contains, Size and Values methods; 2. struct{} as a value type is more efficient than bool because of its zero memory overhead; 3. You can directly use map[string]struct{} to implement simple collection operations; 4. If concurrency security is required, you can combine sync.RWMutex encapsulation; 5. Note that only comparable types can be used as keys, and native map operations are not thread-safe. This method is concise, efficient and in line with Go language habits.
In Go, there's no built-in set data structure, but you can easily implement one using a map with keys of the desired type and struct{} (or bool ) as the value. The most common and idiomatic way is to use map[T]struct{} because struct{} takes up zero bytes, making it memory-efficient.
Here's how you can implement a basic set in Go:
1. Using map[T]struct{} for a Type-Safe Set
type Set[T comparable] struct {
items map[T]struct{}
}
func NewSet[T comparable]() *Set[T] {
return &Set[T]{
items: make(map[T]struct{}),
}
}
func (s *Set[T]) Add(value T) {
s.items[value] = struct{}{}
}
func (s *Set[T]) Remove(value T) {
delete(s.items, value)
}
func (s *Set[T]) Contains(value T) bool {
_, exists := s.items[value]
Return exists
}
func (s *Set[T]) Size() int {
return len(s.items)
}
func (s *Set[T]) Values() []T {
values := make([]T, 0, len(s.items))
for item := range s.items {
values = append(values, item)
}
Return values
}Example Usage
set := NewSet[string]()
set.Add("apple")
set.Add("banana")
set.Add("apple") // Duplicate, will be ignored
fmt.Println(set.Contains("apple")) // true
fmt.Println(set.Size()) // 2
set.Remove("apple")
fmt.Println(set.Contains("apple")) // false Why struct{} instead of bool ?
-
struct{}takes zero memory , so it's more efficient thanbool(which takes 1 byte). - You're only using the key to represent membership — the value is irrelevant.
Alternative: Simple Map-Based Set (Without Struct)
If you don't need a dedicated type, you can use a raw map:
set := make(map[string]struct{})
// Add
set["hello"] = struct{}{}
// Check
if _, exists := set["hello"]; exists {
// present
}
// Remove
delete(set, "hello")Notes
- Go generics (introduced in 1.18) allows you to make the set reusable for any comparable type.
- Only comparable types can be keys in maps (so you can't use slices, maps, or functions in a set).
- This implementation is not thread-safe. For concurrent use, wrap it with a
sync.RWMutex.
Thread-Safe Version (Optional)
import "sync"
type ConcurrentSet[T comparable] struct {
items map[T]struct{}
mu sync.RWMutex
}
func (s *ConcurrentSet[T]) Add(value T) {
s.mu.Lock()
defer s.mu.Unlock()
s.items[value] = struct{}{}
}
func (s *ConcurrentSet[T]) Contains(value T) bool {
s.mu.RLock()
defer s.mu.RUnlock()
_, exists := s.items[value]
Return exists
} Basically, use map[T]struct{} with generics to make a clean, reusable, and efficient set. It's simple, fast, and idiomatic Go.
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