Android Retrofit入队方法未返回值

fun getSurvey() : MutableList<SurveyMaster>{
        //Retrofit creates implementation for this method getSurveyList()
        val call : Call<List<SurveyMaster>> = retrofitPlaceHolderAPI.getSurveyList("bearer "+customIDToken)

        val surveyList =   mutableListOf<SurveyMaster>()

        //enqueue - executing on the background thread, to execute asynchronously
        call.enqueue(object : Callback<List<SurveyMaster>>{
            override fun onFailure(call: Call<List<SurveyMaster>>, t: Throwable) {
                Log.e("Error", t.message)
                //Log.e("Error", t.localizedMessage)
            }

            override fun onResponse(call: Call<List<SurveyMaster>>, response: Response<List<SurveyMaster>>) {
                if (!response.isSuccessful){
                    Log.e("SurveyList Error", "code: "+response.code())
                    return
                }

                val surveys = response.body()

                for(element in surveys!!){
                    surveyList.add(element)
                }
            }
        })
        return surveyList
    }

Enqueue方法在后台线程上运行,但是如何在enqueue方法中返回列表。上面的代码返回空列表。提前致谢