inject

Go-inject — Dependency Injection Library for Go

A dependency injection system for Go inspired by Guice. See the post for detailed guide.

Installation

Go get

go get github.com/monnoroch/go-inject

Dep

dep ensure -add github.com/monnoroch/go-inject

Examples

Inject an int value

Here's a simple module with a single provider:

import (
	"github.com/monnoroch/go-inject"
)

type singleValue struct{}

type MyModule struct{}

func (_ MyModule) ProvideValue() (int, singleValue) {
	return 10, singleValue{}
}

func main() {
	injector, _ := inject.InjectorOf(MyModule{})
	// Will be 10.
	value := injector.MustGet(new(int), singleValue{}).(int)
}

Dependencies

Let's add a second provider that depends on the first one:

type doubleValue struct{}

func (_ MyModule) ProvideValueDouble(value int, _ singleValue) (int, doubleValue) {
	return value * 2, doubleValue{}
}

func main() {
	injector, _ := inject.InjectorOf(MyModule{})
	// Will be 20.
	value := injector.MustGet(new(int), doubleValue{}).(int)
}

Cross-module dependencies

Let's add a second module, which can depend on values provided by the first module:

type tripleValue struct{}

type MyAnotherModule struct{}

func (_ MyAnotherModule) ProvideValue(
	value int, _ singleValue,
	doubledValue int, _ doubleValue,
) (int, tripleValue) {
	return doubledValue + value, tripleValue{}
}

func main() {
	injector, _ := inject.InjectorOf(
		MyModule{},
		MyAnotherModule{},
	)
	// Will be 30.
	value := injector.MustGet(new(int), tripleValue{}).(int)
}

Lazy dependencies

You can inject a function that returns a value. That way the value will be computed lazily.

type tripleValueLazy struct{}

func (_ MyAnotherModule) ProvideValueLazy(
	value int, _ singleValue,
	doubledValue func() int, _ doubleValue,
) (int, tripleValueLazy) {
	return doubledValue() + value, tripleValueLazy{}
}

func main() {
	injector, _ := inject.InjectorOf(
		MyModule{},
		MyAnotherModule{},
	)
	// Will be 30.
	value := injector.MustGet(new(int), tripleValueLazy{}).(int)
}

Auto injecting dependencies in struct fields

import (
	"github.com/monnoroch/go-inject"
	"github.com/monnoroch/go-inject/auto"
)

type MyStruct struct {
	Value        int
	DoubledValue int
}

type myAnnotation struct{}

func main() {
	injector, _ := inject.InjectorOf(
		MyModule{},
		autoinject.AutoInjectModule(new(MyStruct)).
			WithAnnotation(myAnnotation{}).
			WithFieldAnnotations(struct {
				Value        singleValue
				DoubledValue doubleValue
			}{}),
	)
	// Will be MyStruct{Value: 10, DoubledValue: 20}.
	value := injector.MustGet(new(MyStruct), myAnnotation{}).(MyStruct)
}

You can also inplement autoinject.AutoInjectable to provide default way to construct MyStruct:

func (self MyStruct) ProvideAutoInjectAnnotations() interface{} {
	return struct {
		Value        singleValue
		DoubledValue doubleValue
	}{}
}

func main() {
	injector, _ := inject.InjectorOf(
		MyModule{},
		autoinject.AutoInjectModule(new(MyStruct)).
			WithAnnotation(myAnnotation{}),
	)
	// Will be MyStruct{Value: 10, DoubledValue: 20}.
	value := injector.MustGet(new(MyStruct), myAnnotation{}).(MyStruct)
}

You can also use the default autoinject.Auto annotation to simplify code even further:

func main() {
	injector, _ := inject.InjectorOf(
		MyModule{},
		autoinject.AutoInjectModule(new(MyStruct)),
	)
	// Will be MyStruct{Value: 10, DoubledValue: 20}.
	value := injector.MustGet(new(MyStruct), autoinject.Auto{}).(MyStruct)
}

Other features

Providing singletons, private providers, annotation rewriting, dynamic modules and other features are explained in more detail in the guide.