如何在Kotlin中聲明一個包含泛型類型字段的類？

Question

在Kotlin我有一個數據類。

data class APIResponse<out T>(val status: String, val code: Int, val message: String, val data: T?) 

我要聲明另一個類，包括這個：

class APIError(message: String, response: APIResponse) : Exception(message) {} 

但錯誤科特林所賜：預計類APIResponse一類的說法在com.mypackagename

在Java中，我可以定義請執行以下操作：

class APIError extends Exception { 

    APIResponse response; 

    public APIError(String message, APIResponse response) { 
     super(message); 
     this.response = response; 
    } 
} 

如何將代碼轉換爲Kotlin？

Answer 1

你在Java中有什麼是原始類型。在上star-projections的部分，在科特林文件說：

Note: star-projections are very much like Java's raw types, but safe.

他們描述他們的用例：

Sometimes you want to say that you know nothing about the type argument, but still want to use it in a safe way. The safe way here is to define such a projection of the generic type, that every concrete instantiation of that generic type would be a subtype of that projection.

你APIError類，因此就變成了：

class APIError(message: String, val response: APIResponse<*>) : Exception(message) {}