Example of dependency injection in action

di_3.go

package di

import (
        "fmt"
        "regexp"
)

// This is a pretty dumb function. It can only works                                                                 
// if you want to stay with "Hello" forever.                                                                         
func PrintIfMatchedHello(msg string) {
        if msg == "Hello" {
                fmt.Println(msg)
        }
}

// Better, but still quite dumb.                                                                                     
func PrintIfMatchedString(msg, matcher string) {
        if msg == matcher {
                fmt.Println(msg)
        }
}

// You might think regex is the way                                                                                  
func PrintIfMatchedPattern(msg, pattern string) {
        matched, err := regexp.MatchString(pattern, msg)
	if err != nil {
		panic(err)
	}
        if matched {
		fmt.Println(msg)
	}
}

// But, hey, Go has a first-class function! Why not                                                                  
// go for a full inversion of control?                                                                               
func PrintIfMatched(msg string, matcher func(string) bool) {
        if matcher(msg) {
                fmt.Println(msg)
        }
}