go-kid/ioc

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go-kid/ioc is a Go runtime dependency injection (IoC/DI) framework based on tag + interface.

✨ Features

• Component Dependency Injection (wire tag)
  • Inject by pointer type, interface type, or component name
  • Multiple implementation selection strategies (Primary/Qualifier)
  • Inject into interface slices/arrays
• Configuration Injection (value / prop / prefix tags)
  • Multiple configuration sources (command-line args, files, raw content)
  • Configuration placeholders ${...}
  • Expression evaluation #{...} (arithmetic, logical, conditional, collection operations)
• Lifecycle Management: ApplicationRunner, CloserComponent, LazyInitComponent
• context.Context lifecycle support: WithContext variants for all lifecycle interfaces
• Scope mechanism: Singleton/Prototype
• Conditional component registration: Register components based on runtime conditions
• Application event mechanism: Publish and listen for application events
• log/slog adapter support: Integrate with Go's structured logging

📦 Installation

Requires Go 1.21+.

go get github.com/go-kid/ioc

🚀 Quick Start

package main

import (
	"fmt"
	"github.com/go-kid/ioc"
)

// Component to be injected
type ComponentA struct {
	Name string
}

func (a *ComponentA) GetName() string {
	return a.Name
}

// Target struct that depends on ComponentA
type App struct {
	ComponentA *ComponentA `wire:""` // pointer + exported field + wire tag
}

func main() {
	a := new(App)

	// Register components
	ioc.Register(a)
	ioc.Register(&ComponentA{Name: "Comp-A"})

	// Run the framework
	_, err := ioc.Run()
	if err != nil {
		panic(err)
	}

	// Output: "Comp-A"
	fmt.Println(a.ComponentA.GetName())
}

Key points: Dependency fields must be exported (start with uppercase) and use wire:"" to declare injection.

📖 Documentation

1. Component Dependency Injection (wire tag)

Component injection is controlled via tag: wire:"<name>,arg1=xxx,arg2=yyy"

• <name>: optional, inject by component name
• ,arg=...: optional extra arguments (e.g., qualifier)
• wire:"" (empty) means inject by type

Inject by Pointer Type

type Component struct {
	Name string
}

type App struct {
	C *Component `wire:""` // injected by *Component type
}

Inject by Interface Type

type IComponent interface {
	GetName() string
}

type ComponentA struct{ Name string }
func (a *ComponentA) GetName() string { return a.Name }

type App struct {
	C IComponent `wire:""` // inject by interface type
}

Inject by Name

Implement NamingComponent interface to define component names:

type ComponentA struct {
	Name          string
	componentName string
}

func (a *ComponentA) Naming() string { return a.componentName }

type App struct {
	ByName IComponent `wire:"comp-A"` // inject by component name
}

Multiple Implementation Selection Strategy

When an interface has multiple implementations, the container selects by priority:

1. Components implementing WirePrimary interface (primary)
2. Components without alias (not implementing Naming())
3. One will be chosen (order not guaranteed)

Using Primary marker:

type ComponentA struct {
	Name string
	definition.WirePrimaryComponent // embed Primary component
}

Using Qualifier:

type ComponentA struct {
	qualifier string
}

func (a *ComponentA) Qualifier() string { return a.qualifier }

type App struct {
	C IComponent `wire:",qualifier=comp-A"` // use qualifier
}

Inject into Slice/Array

type App struct {
	All []Interface `wire:""` // all Interface implementations
}

2. Configuration Injection

prefix: Bind Config Prefix

type configA struct {
	B int   `yaml:"b"`
	C []int `yaml:"c"`
}

type App struct {
	A *configA `prefix:"a"` // bind config prefix "a"
}

Configuration (YAML):

a:
  b: 123
  c: [1,2,3,4]

value: Literals / Placeholders / Expressions

type T struct {
	DSN string `value:"${db.dsn}"`           // config placeholder
	Sum int    `value:"#{1+2}"`               // expression
	Str string `value:"foo"`                  // literal
}

prop: Sugar for value

type DBConfig struct {
	DSN string `prop:"db.dsn"` // equivalent to value:"${db.dsn}"
}

Placeholders and Expressions

• ${...}: Configuration placeholder, reads value from config
• #{...}: Expression evaluation, supports arithmetic, logical, conditional, collection operations

Example:

type T struct {
	Arithmetic  int    `value:"#{1+(1*2)}"`                      // 3
	Comparison  bool   `value:"#{1/1==1}"`                       // true
	Conditional string `value:"#{1>2?'a':'b'}"`                  // "b"
	WithConfig  int    `value:"#{${number.val1}+${number.val2}}"` // use config
}

3. Application Startup

Style 1: Use ioc.Run / ioc.Register

ioc.Register(a)
ioc.Register(&ComponentA{Name: "Comp-A"})
_, err := ioc.Run()

Style 2: Work with app.App Directly

application := app.NewApp()
err := application.Run(
	app.SetComponents(...),
	app.SetConfigLoader(loader.NewFileLoader("config.yaml")),
	app.SetConfigBinder(binder.NewViperBinder("yaml")),
)

4. Lifecycle Interfaces

• ApplicationRunner: executed after all components are refreshed
• CloserComponent: Close() called when app stops
• LazyInitComponent: marked as lazy initialization
• PriorityComponent: controls post-processor execution order
• InitializeComponentWithContext / InitializingComponentWithContext: context-aware Init/AfterPropertiesSet
• ApplicationRunnerWithContext: context-aware Run
• CloserComponentWithContext: context-aware Close
• DestructionAwareComponentPostProcessor: callback before created singletons are destroyed
• ScopeComponent: control component scope (singleton/prototype)
• ConditionalComponent: conditional registration based on runtime conditions
• ApplicationEventListener / ApplicationEventPublisher: event mechanism

5. Context Support

All lifecycle interfaces have WithContext variants. Components can implement them to receive a context.Context for timeout control, cancellation propagation, etc.

// Run the framework with a context
app, err := ioc.RunWithContext(ctx)

// Set a shutdown timeout
_, err := ioc.Run(app.SetShutdownTimeout(30 * time.Second))

Context-aware lifecycle interfaces:

// InitializeComponentWithContext (replaces InitializeComponent)
func (c *MyComp) Init(ctx context.Context) error { return nil }

// InitializingComponentWithContext (replaces InitializingComponent)
func (c *MyComp) AfterPropertiesSet(ctx context.Context) error { return nil }

// ApplicationRunnerWithContext (can coexist with ApplicationRunner)
func (r *MyRunner) RunWithContext(ctx context.Context) error { return nil }

// CloserComponentWithContext (can coexist with CloserComponent)
func (c *MyComp) CloseWithContext(ctx context.Context) error { return nil }

Note: Init(ctx) and AfterPropertiesSet(ctx) have the same method names as their base interfaces but different signatures, so a component implements one or the other. RunWithContext and CloseWithContext use distinct method names, allowing a component to implement both the original and context-aware versions.

6. Scope

Control component scope by implementing ScopeComponent:

• Singleton (default): single instance in the container
• Prototype: a new instance is shallow-copied from the registered template and fully populated on every access; it is not eagerly created

import "github.com/go-kid/ioc/definition"

type MyPrototype struct{}

func (p *MyPrototype) Scope() string { return definition.ScopePrototype }

7. Conditional Registration

Implement ConditionalComponent to decide at runtime whether a component should be created:

import "github.com/go-kid/ioc/definition"

type MyComp struct{}

func (c *MyComp) Condition(ctx definition.ConditionContext) bool {
	return ctx.HasComponent("dependency")
}

8. Events

Publish and listen for application events to enable loose coupling between components:

import "github.com/go-kid/ioc/definition"

// Listen for events
type MyListener struct{}

func (l *MyListener) OnEvent(event definition.ApplicationEvent) error {
	// handle event
	return nil
}

Built-in events: ComponentCreatedEvent after a component is initialized, ApplicationStartedEvent after runners complete, and ApplicationClosingEvent before shutdown. On shutdown, destruction-aware post-processors run for created singletons in reverse creation order, then closer components run concurrently. Prototype instances are owned by their callers and are not destroyed automatically.

🏗️ Architecture

┌─────────────────────────────────────────────────────────────────┐
│                          app.App                                 │
│  ┌──────────────────┐              ┌──────────────────┐         │
│  │ Component Factory│              │    Configure     │         │
│  └────────┬─────────┘              └────────┬─────────┘         │
│           │                                  │                   │
│           │                                  │                   │
│  ┌────────▼─────────┐              ┌────────▼─────────┐       │
│  │ DefinitionRegistry│              │      Loader       │       │
│  │ SingletonRegistry│              │  (args/file/raw)  │       │
│  └────────┬─────────┘              └────────┬─────────┘       │
│           │                                  │                   │
│           │ register                         │                   │
│  ┌────────▼─────────┐              ┌────────▼─────────┐       │
│  │ComponentDefinition│              │      Binder       │       │
│  └────────┬─────────┘              │      (viper)       │       │
│           │                         └───────────────────┘       │
│           │ create                                               │
│  ┌────────▼─────────┐                                           │
│  │     Instance     │                                           │
│  └────────┬─────────┘                                           │
│           │                                                      │
│  ┌────────▼──────────────────────────────────────────┐          │
│  │            PostProcessors                          │          │
│  │  ┌────────────────────────────────────────────┐   │          │
│  │  │ • LoggerAware                               │   │          │
│  │  │ • ConfigQuoteAware ${...}                   │   │          │
│  │  │ • ExpressionTagAware #{...}                  │   │          │
│  │  │ • PropertiesAware prefix                    │   │          │
│  │  │ • ValueAware value/prop                     │   │          │
│  │  │ • DependencyAware wire                      │   │          │
│  │  │ • DependencyFunctionAware func               │   │          │
│  │  └────────────────────────────────────────────┘   │          │
│  └──────────────────────────────────────────────────┘          │
└─────────────────────────────────────────────────────────────────┘

Config Flow: Binder → ConfigQuoteAware, PropertiesAware, ValueAware, ExpressionTagAware

📚 Examples & Tests

• Example projects: examples/debug_demo, examples/post_processor
• Post processor example: examples/post_processor/
• Performance tools: cmd/performance_analyst/
• Unit tests: unittest/component/builtin_inject/*, unittest/configure/*

Run tests:

go test ./...

Pull requests and pushes to main also run the race detector, go vet, go build, and enforce at least 75% repository-wide statement coverage in GitHub Actions.

📄 License

MIT License

🤝 Contributing

Contributions via Issues / PRs are welcome. Please ensure go test ./... passes before submitting.

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