Functional Dependency Injection example

simple.go

package main

import "log"

// Our container
type Application struct {
        DB Database
}

// Interface for a system component
type Database struct {
        SampleFunc func() string
}

// General mock implementation
func MockDatabase() Database {
        db := Database{}
        db.SampleFunc = func() string {
                return "base"
        }
        return db
}

func main() {
        db := MockDatabase()
        log.Print(db.SampleFunc())

        db.SampleFunc = func() string {
                return "injected!"
        }
        log.Print(db.SampleFunc())

        a := Application{MockDatabase()}
        log.Print(a.DB.SampleFunc())
        a.DB.SampleFunc = func() string {
                return "injected via app container"
        }
        log.Print(a.DB.SampleFunc())
}