interface_test.go

package main

import (
    "fmt"
)

type Inter interface {
    Func(string)
}

type Impl struct {
    count int
}

func (p *Impl) Func(s string) {
    p.count += 1
    fmt.Println(s)
    return
}

type Service struct {
    handlers []Inter
}

func (p *Service) AppendHandler(i Inter) {
    p.handlers = append(p.handlers, i)
}

func (p *Service) Run() {
    for _, handler := range p.handlers {
        handler.Func("string")
    }
}

func main() {
    var (
        service Service
        impl    Impl
    )

    service.AppendHandler(impl)
    service.Run()
}