Ada通用类型图像属性

Question

我目前正在大学的实时编程语言课程中学习Ada,并对泛型有疑问.

我有一个通用的程序 csv_put

package PSU_Logging is

   type logged_signal_names_t is (
      t,
      U_V1,
      I_L1,
      U_C1,
      I_L2,
      U_C2,
      I_Load
   );

private
   ... Some types, tasks and subprogramms ...

   generic
      type Item_Type_t is private;
      procedure csv_put (File : in File_Type; Item : in Item_Type_t);

end PSU_Logging;

与定义

package body PSU_Logging is

   procedure csv_put (File : in File_Type; Item : in Item_Type_t) is
   begin
      Put (File, Item_Type_t'Image (Item));
      Put (File, ", ");
   end csv_put;

   procedure csv_put_float is new csv_put (Item_Type_t => Float);
   procedure csv_put_duration is new csv_put (Item_Type_t => Duration);
   procedure csv_put_signal_name is new csv_put (Item_Type_t => logged_signal_names_t);

   ... Definition of other things ...

end PSU_Logging;

到现在为止还挺好.太糟糕了,我在编译期间遇到以下错误

Compile
   [Ada]          psu_logging.adb
      psu_logging.adb:9:18: prefix of "image" attribute must be a scalar type or a scalar object name
gprbuild: *** compilation phase failed

有任何想法吗？我以为我可以在通用过程中使用泛型类型,就像任何其他类型一样.由于我的所有实例都使用标量类型,我认为这应该不是问题.

顺便问一下:你最喜欢的Ada教程/参考是什么？我喜欢Ada上的Wikibooks页面,但还没有完成.

Answer 1

一个可能的workround(原谅我的资本重组,这是我的编辑器的设置方式):提供Image一个通用参数,

generic
   type Item_Type_T is private;
   with function Image (Item : Item_Type_T) return String;
procedure Csv_Put (File : in File_Type; Item : in Item_Type_T);

procedure Csv_Put (File : in File_Type; Item : in Item_Type_T) is
begin
   Put (File, Image (Item));
   Put (File, ", ");
end Csv_Put;

并’Image在可用的地方实例化,否则你自己:

procedure Csv_Put_Float is new Csv_Put (Item_Type_T => Float,
                                        Image => Float'Image);