Custom Errors in Ada

Our first example demonstrates how to create custom error types in Ada. This is similar to implementing the Error() method in other languages.

with Ada.Text_IO; use Ada.Text_IO;
with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;

procedure Custom_Errors is
   -- A custom error type usually has the suffix "Error".
   type Arg_Error is record
      Arg     : Integer;
      Message : Unbounded_String;
   end record;

   -- Define an exception for our custom error
   Arg_Error_Exception : exception;

   -- Function to raise our custom error
   function F (Arg : Integer) return Integer is
   begin
      if Arg = 42 then
         -- Raise our custom exception with the error details
         raise Arg_Error_Exception with 
           Integer'Image(Arg) & " - " & To_String(To_Unbounded_String("can't work with it"));
      end if;
      return Arg + 3;
   end F;

begin
   declare
      Result : Integer;
   begin
      Result := F(42);
      Put_Line("Result: " & Integer'Image(Result));
   exception
      when Arg_Error_Exception =>
         -- Extract the error message
         declare
            Error_Message : String := Exception_Message(Arg_Error_Exception'Identity);
         begin
            Put_Line("Caught Arg_Error:");
            Put_Line(Error_Message);
         end;
   end;
end Custom_Errors;

In this Ada example, we define a custom error type Arg_Error as a record. We also define an exception Arg_Error_Exception to represent our custom error condition.

The F function demonstrates how to raise our custom exception when a specific condition is met (in this case, when the argument is 42).

In the main procedure, we call F with the argument 42 and handle the potential exception. If an Arg_Error_Exception is raised, we catch it and print the error message.

To run this program:

$ gnatmake custom_errors.adb
$ ./custom_errors
Caught Arg_Error:
42 - can't work with it

This example shows how Ada handles custom errors through exceptions, which is a bit different from the error interface approach in some other languages. However, it allows for similar functionality in terms of creating and handling custom error types.

Errors in Ada

Goroutines in Ada

Learn X By Example

Title here

Custom Errors in Ada