Go Programming | Instantiating A Singleton Object

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Instantiating a singleton object is a way to ensure that only one instance of a class is created.

I will demonstrate different ways to instantiate a singleton object in this post.

1. Package Level Variable

Variable defined in a package scope is accessible to all the files in the same package. It is helpful to share data between different functions.

We can create a singleton object by assigning a value to a variable in the package scope.

For example:

“abc.go”

package abc
import "time"
var StartTime = time.Now()

“main.go”

package main
import (
    "fmt"
    "time"
    "example.com/m/abc"
)
func main() {
    fmt.Println(abc.StartTime)
    time.Sleep(1 * time.Second)
    fmt.Println(abc.StartTime)
}

“result”:

2022-05-10 11:58:06.076867 +0800 CST m=+0.000095853
2022-05-10 11:58:06.076867 +0800 CST m=+0.000095853

As our expectation, the singleton objectStartTime is the same in two consecutive calls.

2. init function

The functioninit is a predefined function that is called when the package is imported. It is typically used to initialize a specific state of the package.

“abc.go”

package abc
import "time"
var StartTime time.Time

func init() {
    StartTime = time.Now()
}

3. A function call from in the Main function

At the start of the main function, we call the initApp function to initialize some variables.

“main.go”

package main
import (
    "fmt"
    "time"
    )
var startTime time.Time
func initApp() {
    startTime = time.Now()
}
func main() {
    initApp()
    
    fmt.Println(startTime)
}