为了使用多态性，可以在Ada中实例化一个带有标记记录类型的Map容器​​？

Question

我想有一个地图容器，其中将包含一个标签的记录类型，所以我写了这个程序，但GNAT编译器不会编译：

type http_response is tagged private; 
package map_package is new Ada.Containers.Ordered_Maps 
    (Key_Type => Unbounded_String, 
    Element_Type => http_response); 

我也有那些编译错误：

http.ads:47:04: instantiation error at a-coorma.ads:199 
http.ads:47:04: premature use of type with private component 
http.ads:47:105: premature use of private type 

确实我想使用多态，因为我的地图将包含其他标记的记录类型，它从http_response类型继承。

如何改正这段代码？

如果我纠正这样的代码：

package map_package is new Ada.Containers.Ordered_Maps 
    (Key_Type => Unbounded_String, 
    Element_Type => http_response'Class); 

我得到这样的错误：

http.ads:47:04: instantiation error at a-coorma.ads:195 
http.ads:47:04: class-wide subtype with unknown discriminants in component declaration 
http.ads:47:04: instantiation error at a-coorma.ads:199 
http.ads:47:04: premature use of type with private component 
http.ads:47:118: premature use of type with private component 

Answer 1

正如3.3 Objects and Named Numbers提到，“A类范围的子类型被定义为具有未知的判别，因此是一个不确定的子类型。“而不是Ada.Containers.Ordered_Maps，您可能能够实例化Ada.Containers.Indefinite_Ordered_Maps。