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Singleton Provider #291
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Hello @ehsannm.
All functions provided to Dig/Fx are treated as singletons and re-used in every other function.For example, if you have,
func NewFoo() *Foo { fmt.Println("building Foo") return // ... }And you use that with two constructors
NewBar(*Foo) *BarandNewBaz(*Foo) *Bar,
both Dig and Fx will instantiate*Fooonly once (calling that print statement only once)
and share it between Bar and Baz.Sample code with Dig (run it at https://play.golang.org/p/bHol91PaDj3):
package main import ( "fmt" "go.uber.org/dig" ) type Foo struct{} func NewFoo() *Foo { fmt.Println("building Foo") return new(Foo) } type Bar struct{} func NewBar(*Foo) *Bar { fmt.Println("using Foo in Bar") return new(Bar) } type Baz struct{} func NewBaz(*Foo) *Baz { fmt.Println("using Foo in Baz") return new(Baz) } func main() { c := dig.New() if err := c.Provide(NewFoo); err != nil { panic(err) } if err := c.Provide(NewBar); err != nil { panic(err) } if err := c.Provide(NewBaz); err != nil { panic(err) } if err := c.Invoke(run); err != nil { panic(err) } } func run(bar *Bar, baz *Baz) { fmt.Println("running application") }
Closing because answered.
If I misunderstood the question, feel free to open a new issue with more details.
Thanks!- locked and limited conversation to collaborators
on Aug 16, 2022
Is there anyway to make a provider function as singleton ?
There are cases we have one dependency object which must be initialized only once but is used by many other objects.
How to handle those cases in uber/dig ?