How to implement a set data structure efficiently in Go?
Jul 25, 2025 am 03:58 AM
Go does not have a built-in collection type, but it can be implemented efficiently through maps. Use map[T]struct{} to store element keys, empty structures have zero memory overhead, and the implementation of addition, inspection, deletion and other operations are O(1) time complexity; in a concurrent environment, sync.RWMutex or sync.Map can be combined to ensure thread safety; in terms of performance, memory usage, hashing cost and disorder; it is recommended to encapsulate Add, Remove, Contains, Size and other methods to simulate standard collection behavior.
In Go, there's no built-in set data structure like in Python or JavaScript, but implementing one efficiently is straightforward using a map. The key idea is to use the keys of a map to represent the set elements, and ignore the values (or use them as placeholders).
Here's how you can do it effectively.
Use a Map with Empty Struct Values
The most common and memory-efficient way to implement a set in Go is by using a map[T]struct{} where T is the type of your elements.
Why struct{} ? Because it takes up zero memory when stored as a value in a map, which makes this approach more efficient than using bool or other types.
set := make(map[int]struct{})To add an element:
set[5] = struct{}{}To check if an element exists:
if _, exists := set[5]; exists {
// do something
}This method keeps memory usage low and operations fast — all basic set operations (insert, delete, lookup) are O(1) time complexity.
Handle Thread Safety for Concurrent Use
If you're working in a concurrent environment (eg, multiple goroutines accessing the set), standard maps aren't safe for concurrent reads and writes.
You have two main options:
- Wrap your map with a
sync.RWMutexto control access. - Use
sync.Mapif your workload involves mostly insertions and looksups with few deletions, though it may not always be the best fit.
Using a mutex-based wrapper looks like this:
type Set struct {
m map[int]struct{}
mu sync.RWMutex
}
func (s *Set) Add(val int) {
s.mu.Lock()
defer s.mu.Unlock()
sm[val] = struct{}{}
}
func (s *Set) Contains(val int) bool {
s.mu.RLock()
defer s.mu.RUnlock()
_, exists := sm[val]
Return exists
}For single-threaded use or read-heavy workloads, stick with a plain map — it's faster and simpler.
Consider Performance Trade-offs
While the map-based approach is simple and fast, there are a few performance-related considerations:
- Memory overhead : Maps store both keys and values, so even though
struct{}adds nothing, the key itself still contributes to memory usage. - Hashing cost : Every operation requires hashing the key, so if you're storing large structs as keys (not common), consider wrapping them in a pointer or flattening them.
- Iteration order : Sets implemented via maps don't maintain any order. If you need ordered traversal, you'll have to collect the keys into a slice and sort them manually.
If you're dealing with integers and performance is critical, some people use bitset implementations for dense integer ranges. But those are less flexible and not suitable for sparse or non-integer sets.
Bonus: Basic Operations You'll Want to Implement
Here are a few helper functions you might want to write for your set:
- Add : Insert a new item
- Remove : Delete an existing item
- Contains : Check exists
- Size : Return number of elements
- Clear : Reset the set
- Items : Get a slice of all items (optional)
func (s *Set) Remove(val int) {
s.mu.Lock()
defer s.mu.Unlock()
delete(sm, val)
}
func (s *Set) Size() int {
return len(sm)
}These extensions help mimic typical set behavior found in other languages.
That's basically it — Go doesn't have a native set, but using a map gives you a clean and perform alternative. It's simple enough for most use cases and easy to customize when needed.
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