Starting from go1.18, Go will officially support generic. This package is designed to embrace the new technic for convenience.
Call Singleton with a given type name to get a pointer to this type.
type MyType struct {
field int
}
v1 := singleton.Singleton[MyType]()
v1.field = 123
v2 := singleton.Singleton[MyType]()
println(v2.field) // Output: 123