我已经编写了用于会计系统访问的界面。我想从我的程序中隐藏接口的特定实现，因为我将永远只有一个“活动的”记帐系统。因此，我计划将接口的方法设置为不导出（隐藏），然后导出基本包中固有的导出函数，这些函数从本地适配器调用相同的函数。

package accounting

import "errors"

type IAdapter interface {
    getInvoice() error
}

var adapter IAdapter

func SetAdapter(a IAdapter) {
    adapter = a
}

func GetInvoice() error {
    if (adapter == nil) {
        return errors.New("No adapter set!")
    }
    return adapter.getInvoice()
}


__________________________________________________

package accountingsystem

type Adapter struct {}

func (a Adapter) getInvoice() error {return nil}


__________________________________________________


package main

import (
    "accounting"
    "accountingsystem"
)

function main() {
    adapter := accountingsystem.Adapter{}
    accounting.SetAdapter(adapter)
}

问题在于，由于无法看到getInvoice()by 的实现，编译器会抱怨accountingsystem.Adapter：

./main.go:2: cannot use adapter (type accountingsystem.Adapter) as type accounting.IAdapter in argument to accounting.SetAdapter:
accountingsystem.Adapter does not implement accounting.IAdapter (missing accounting.getInvoice method)
    have accountingsystem.getInvoice() error
    want accounting.getInvoice() error

有什么方法可以用另一个包中的未导出方法实现接口？还是我以一种非惯常的方式思考这个问题？