What is the singleton pattern in golang and is it an anti-pattern
Jul 11, 2025 am 02:08 AM
Singleton mode is implemented in Go through package-level variables and functions, ensuring that a type has only one instance and provides a global access point. 1. Use private variables and public access functions to achieve lazy loading; 2. Ensure concurrency security through sync.Once; 3. Commonly used in configuration management, database connection and other scenarios. Although singletons are often regarded as anti-pattern due to problems such as introducing global state and hidden dependencies, they are still applicable in small projects or performance-sensitive scenarios. Dependency injection should be considered if multiple instances are needed to be maintained.
Singleton pattern in Go is a design pattern that ensures a type has only one instance and provides a global point of access to it. It's commonly used for things like configuration managers, database connections, or logging systems — places where having multiple instances could lead to inconsistency or unnecessary overhead.
In Go, since there's no class structure like in traditional object-oriented languages, the singleton pattern is usually implemented using package-level variables and functions. The most straightforward way is to use a private variable combined with a public function to access it.
How to implement singleton in Go
Go doesn't enforce access modifiers like private or public , but by convention, identifiers starting with lowercase are considered unexported (private), while uppercase ones are exported (public). This allows us to control instantiation.
Here's a basic example:
package singleton
type Config struct {
Data string
}
var config *Config
func GetConfig() *Config {
if config == nil {
config = &Config{
Data: "default",
}
}
return config
} This implementation uses lazy initialization — the instance is created only when GetConfig() is first called.
Note: In concurrent environments, you should protect this with synchronization. You can use
sync.Onceto make sure the initialization happens exactly once:
var (
config *Config
once sync.Once
)
func GetConfig() *Config {
once.Do(func() {
config = &Config{
Data: "default",
}
})
return config
}This ensures thread safety without overcomplicating the logic.
Why some consider singleton an anti-pattern
While the singleton pattern is useful, it often gets criticalized for these reasons:
- Global state : Like global variables, singletons introduce shared state across your application, which can make testing and debugging harder.
- Hidden dependencies : When a function relies on a singleton, it's not immediately clear from its signature what dependencies it needs.
- Harder to mock : In unit tests, replacing a singleton with a mock or stub is more complicated than passing in a dependency.
- Limits flexibility : If later you decide you need multiple instances (eg, different configs for different tenants), the singleton becomes a hurdle.
For example, imagine a logger singleton used throughout your app. If you want to test how your code behaves with different log levels or outputs, it's easier if each component receives a logger interface rather than pulling from a global instance.
When it's OK to use singleton in Go
Although the downsides, there are situations where the singleton pattern makes sense in Go:
- Package-level utilities : For types that truly need only one instance, like a connection pool or a configuration loader.
- Performance-sensitive scenarios : Avoiding repeated creation of expensive objects (like DB connections) can be a valid use case.
- Simple applications : In smaller projects, strict dependency injection might feel like overkill.
Still, even in those cases, it's worth considering whether the singleton can be wrapped behind an interface so it's easier to replace later.
If you're building something small or performance-critical, go ahead and use a singleton. But for larger systems, especially ones that aim to be maintained and testable, prefer dependency injection over global access points.
Basically that's it.
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