What is the empty struct struct{} used for in Golang
Sep 18, 2025 am 05:47 AM
struct{} is a structure without fields in Go, which occupies zero bytes and is often used in scenarios where data is not required. It is used as a signal in the channel, such as goroutine synchronization; 2. Used as a collection of value types of maps to achieve key existence checks in efficient memory; 3. Definable stateless method receivers, suitable for dependency injection or organization functions. This type is widely used to express control flow and clear intentions.
In Go, the empty struct , written as struct{} , is a struct type with no fields. It takes up zero bytes of storage and is often used when you need to signal an event or represent present without carrying any data.
1. As a placeholder in channels
When using channels for signaling (not transferring data), struct{} is ideal because it conveys intent clearly and uses no memory:
<br>done := make(chan struct{})<br><br> go func() {<br> // do some work<br> close(done)<br> }()<br><br> This pattern is common in goroutine synchronization. Using struct{} instead of bool or int makes it clear no value is being sent—only a signal.
2. For managing sets with map keys
Go doesn't have built-in set types. A common idiom is using a map[T]struct{} to emulate a set of values:
<br>set := make(map[string]struct{})<br><br> set["hello"] = struct{}{}<br> set["world"] = struct{}{}<br><br> // Check membership<br> if _, exists := set["hello"]; exists {<br> // key is present<br> }<br> The struct{} as value takes zero space, making this approach memory-efficient. The focus is on key presence, not the associated value.
3. To define method receivers without data
You can define methods on struct{} if you want a type with behavior but no state:
<br>type worker struct{}<br><br> func (w worker) Process() {<br> // perform task<br> }<br>This is less common but useful in dependency injection or when organizing functions under a named type without needing fields.
Basically, struct{} is a lightweight, zero-memory way to express structure or control flow in Go. It's widely used in idiomatic code for signaling, sets, and clean APIs.
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