Vessel

Vessel is a standalone, type-safe dependency injection container for Go. It provides constructor-based injection, service lifecycle management, flexible resolution strategies, and support for lazy and optional dependencies. Vessel is the DI engine that powers Forge, but it can be used independently in any Go project.

Installation01

go get github.com/xraph/vessel

Recommended Pattern02

Use constructor injection by type as the default pattern. Dependencies are resolved automatically from function parameter types.

import "github.com/xraph/vessel"

c := vessel.New()

vessel.Provide(c, func() *Database {
    return &Database{DSN: "postgres://localhost:5432/app"}
})

vessel.Provide(c, func(db *Database) *UserService {
    return &UserService{db: db}
})

// Resolve by type -- no string keys needed
userService, err := vessel.Inject[*UserService](c)

This keeps your dependency graph explicit, avoids string-key drift, and provides compile-time type safety.

Key Features03

• Type-safe generics -- compile-time type checking via Go generics

• Constructor injection -- automatic dependency resolution with In/Out structs

• Multiple lifecycles -- singleton, transient, and scoped services

• Named instances -- WithName and WithAliases for multiple instances of the same type

• Lazy and optional dependencies -- Lazy[T], OptionalLazy[T], Provider[T]

• Service lifecycle -- built-in Start/Stop/Health management with topological ordering

• Circular dependency detection -- detected at resolution time with clear error paths

• Concurrency safe -- thread-safe container operations

• Middleware hooks -- intercept resolve and lifecycle events

• Service discovery -- query and filter services by lifecycle, group, or metadata

Documentation04