Exception Not Handled (ENH)

Description:

It simplifies programming but does not make it possible for the compiler to detect unhandled exceptions. ENH tries to detect such problems by building a method call closure and propagating thrown exceptions. ENH considers only exceptions explicitly generated by a program (using the raise statement) and not runtime exceptions caused by system methods, such as invalid array index or null reference exceptions. Unfortunately, it is not clear when an exception has to be caught and handled, so error messages are produced by ENH in two situations:

• An exception is not handled in the main method (so this exception can cause termination of the program).
• An exception is not caught in the try-except statement (so the try-except statement handles some other exception, but not this one).

Incorrect:

type

  NoSuchFileException = class(System.Exception)
  end;

  CorruptedFileException = class(System.Exception)
  end;

  VersionNotSupportedException = class(System.Exception)
  end;

  Database = class

    private
    const SupportedVersion: String = '3.0';

    public
    procedure Open(fileName:String);
    function OpenFile(fileName:String):boolean;
    function ReadHeader():boolean;

    procedure set_Version(const ver: String);
    function get_Version(): String;
    property Version:String read get_Version write set_Version;
    end;

  MyApplication = class

    public
        class procedure Main(args: array of String);
  end;
...
procedure Database.Open(fileName:String);
begin
  if not OpenFile(fileName) then
    raise NoSuchFileException.Create();
  if not ReadHeader() then
    raise CorruptedFileException.Create;
  if Version < SupportedVersion then
    raise VersionNotSupportedException.Create;
end;

class procedure MyApplication.Main(args: array of String);
var db:Database;
begin
  db := Database.Create;
  try
    db.Open(args[0]);
  except
    on NoSuchFileException do
       System.Console.WriteLine('File not found');
  end;
end;

Correct:

class procedure MyApplication.Main(args: array of String);
var db:Database;
begin
  db := Database.Create;
  try
    db.Open(args[0]);
  except
    on NoSuchFileException do
       System.Console.WriteLine('File not found');
    on CorruptedFileException do
       System.Console.WriteLine('File is corrupted');
    on VersionNotSupportedException do
       System.Console.WriteLine('Version is not supported');
  end;
end;