如何在Kotlin中声明一个包含泛型类型字段的类？

Question

在Kotlin我有一个数据类。

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

我要声明另一个类，包括这个：

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

但错误科特林所赐：预计类APIResponse一类的说法在com.mypackagename

在Java中，我可以定义请执行以下操作：

class APIError extends Exception { 

    APIResponse response; 

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

如何将代码转换为Kotlin？

Answer 1

你在Java中有什么是原始类型。在上star-projections的部分，在科特林文件说：

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

他们描述他们的用例：

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类，因此就变成了：

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