How to implement a set data structure in Go?
Jul 23, 2025 am 02:34 AM
In Go, there is no built-in set type, but a set can be efficiently implemented using a map with struct{} values to minimize memory usage. 1. Use a map[T]struct{} to represent a set where keys are the elements. 2. Perform add operations by assigning a key to struct{}. 3. Check existence using the comma-ok idiom. 4. Remove elements with delete(). 5. Wrap operations in helper functions or types like StringSet for readability. 6. For concurrency, use a mutex-protected struct or sync.Map. 7. Optionally use third-party packages like golang-set for advanced features at the cost of some type safety and performance. This approach offers a simple, efficient, and flexible way to work with sets in Go.
In Go, there's no built-in set type, but implementing one is straightforward using a map. The idea is to use the keys of a map to represent the elements of the set, and since we don't care about the values, we can use a struct{} to keep memory usage minimal.
Using a Map as a Set
The most common way to implement a set in Go is by using a map[T]struct{}. This leverages the efficiency of maps for lookups, insertions, and deletions, which are all O(1) on average.
For example:
set := make(map[string]struct{})
set["a"] = struct{}{}
set["b"] = struct{}{}To check if an element exists:
if _, exists := set["a"]; exists {
// "a" is in the set
}To remove an element:
delete(set, "a")
This approach works for any comparable type — strings, integers, structs (as long as they contain only comparable fields), etc.
Basic Set Operations
Here are some common operations you might want in a set:
- Add: Insert a new element
- Remove: Delete an existing element
- Contains: Check if an element exists
- Size: Get the number of elements
- Clear: Remove all elements
You can wrap these into a type alias and helper functions for better readability and reusability.
Example:
type StringSet map[string]struct{}
func (s StringSet) Add(value string) {
s[value] = struct{}{}
}
func (s StringSet) Contains(value string) bool {
_, exists := s[value]
return exists
}This makes your code cleaner and gives you a more intuitive interface to work with.
Handling Thread Safety (Optional)
If you're working in a concurrent environment, the built-in map isn't thread-safe. So you’ll need to add a mutex to protect access.
You can do this by defining a struct that includes a map and a mutex:
type ConcurrentSet struct {
m map[string]struct{}
mu sync.Mutex
}
func (cs *ConcurrentSet) Add(value string) {
cs.mu.Lock()
defer cs.mu.Unlock()
cs.m[value] = struct{}{}
}
func (cs *ConcurrentSet) Contains(value string) bool {
cs.mu.Lock()
defer cs.mu.Unlock()
_, exists := cs.m[value]
return exists
}This ensures safe access from multiple goroutines, but it comes with a small performance cost. Only use this if concurrency is needed.
Consider Using a Helper Package
While it’s easy to roll your own basic set, some developers prefer using well-tested packages like golang-set, which provides a more feature-rich and generic-like interface.
These packages often support operations like union, intersection, and difference out of the box. But keep in mind that they usually rely on interface{} and type assertions, which can be less performant and type-safe than using native maps.
So if you want:
- Simplicity and type safety → stick with a native map-based set
- Advanced set operations → consider a third-party package
- Concurrent access → wrap your set with a mutex or use a sync.Map
That's the core of how to work with sets in Go. It’s not fancy, but using maps gives you a solid, readable, and efficient solution.
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