如何检查输入是否为枚举类型

Question

我正在读取键盘输入。输入应该匹配枚举类型中定义的元素之一。这是枚举类型的示例：

type NameType is (Bob, Jamie, Steve);

如果我收到的输入不是这 3 个之一，Ada 会引发 IO 异常。我该如何处理这个问题，以便我可以简单地显示“重试”消息而不让程序停止？

Answer 1

您可以尝试进行未经检查的转换，将值放入 NameType 的变量中，然后对该变量调用“有效”。

编辑以包含来自 ADAIC

的示例

with Ada.Unchecked_Conversion;
with Ada.Text_IO;
with Ada.Integer_Text_IO;

procedure Test is

   type Color is (Red, Yellow, Blue);
   for Color'Size use Integer'Size;

   function Integer_To_Color is
      new Ada.Unchecked_Conversion (Source => Integer,
                                    Target => Color);

   Possible_Color : Color;
   Number         : Integer;

begin  -- Test

   Ada.Integer_Text_IO.Get (Number);
   Possible_Color := Integer_To_Color (Number);

   if Possible_Color'Valid then
      Ada.Text_IO.Put_Line(Color'Image(Possible_Color));
   else
      Ada.Text_IO.Put_Line("Number does not correspond to a color.");
   end if;

end Test;

Answer 2

创建 Enumeration_IO for Name_Type, say Name_IO. In a loop, enter a nested block to handle any Data_Error that arises. When Name_IO.Get succeeds, exit 的实例 loop。

with Ada.IO_Exceptions;
with Ada.Text_IO;

procedure Ask is

type Name_Type is (Bob, Jamie, Steve);
package Name_IO is new Ada.Text_IO.Enumeration_IO (Name_Type);

begin
   loop
      declare
         Name : Name_Type;
      begin
         Ada.Text_IO.Put("Enter a name: ");
         Name_IO.Get(Name);
         exit;
      exception
         when Ada.IO_Exceptions.Data_Error =>
            Ada.Text_IO.Put_Line("Unrecognized name; try again.");
      end;
   end loop;
end Ask;

替代方法包括：

Name_Type'Value，定义为here and illustrated .
Enumeration_IO.Get，定义为here and discussed here.

如何检查输入是否为枚举类型

How to check if input is an enumeration type

enumeration

ada