package main

log = logmain.New(...)

package lib

func Test() {
  log = ?
}

package lib

type Work struct {
  log *log.Logger
}

func (m *Work) Test() {
  m.log.Print(...)
}

type Logger interface {
    Printf(string, ...interface{})
}

type Foo struct {
    logger Logger
}

func NewFoo(logger Logger) *Foo {
    return &Foo{
        logger: logger,
    }
}