ada - 在 Ada(2005 或 2012)中实现与 java finalize block 等效的最佳实践

Question

Java 有一个 finalize 块，它允许在一个块之后执行一些语句
离开(即使引发异常也会执行)。例子:

try {
  ...
} catch (Exception e) {
  ...
} finally {
  ... // any code here
}

Ada 拥有允许实现 的受控对象。敲定 手术
但是没有与 java 中相同的 finalize 块。这对记录很有用，
关闭文件、交易等(无需为每个可能的块创建特定的标记类型)。

您将如何在 Ada 2005 中实现这样的 finalize 块(同时保持代码可读)？

Ada 2012 中是否有允许轻松执行任何终结代码的计划？

Answer 1

正如 Adrien 在评论中提到的，Finalize更类似于析构函数。

要获得近似异常/最终序列的东西，您可以按照这些方式做一些事情( 警告，未编译，只需输入 -- 我们将一起解决任何错误 :-) 另请参阅 Exceptions section的 Ada RM。

with Ada.Exceptions;  use Ada.Exceptions;

procedure Do_Something is

   -- Variables and what-not...

   -- In case you have an exception and want to reraise it after you've done
   -- the 'final' processing.
   Exception_Caught : Exception_Occurrence := Null_Occurrence;

begin
   -- You can have some statements, like initializations, here that will not
   -- raise exceptions.  But you don't have to, it can all just go in the
   -- following block. However you want to do it...

   declare
      -- If you need to declare some entities local to a block, put those here.
      -- If not, just omit this declare section.  Be aware, though, that if
      -- you initialize something in here and it raises an exception, the
      -- block's exception handler will not catch it. Such an exception will
      -- propagate out of the whole procedure (unless it has an outermost
      -- exception handler) because you're _not_ in the block's scope yet.

   begin
      -- Main processing that might raise an exception

      ...

   exception
      when E : others =>
         -- Handle any exception that's raised.  If there are specific
         -- exceptions that can be raised, they should be explicitly
         -- handled prior to this catch-all 'others' one.

         -- Save the exception occurrence, i.e. make a copy of it that can
         -- be reraised in the 'Final' section if needed.  (If you want to
         -- reraise for a specific exception, do this in those handlers as
         -- well.
         Save_Occurrence(Exception_Caught, E);

   end;

   -- Final processing. Everything from here to the end of the procedure is
   -- executed regardless of whether an exception was raised in the above
   -- block.  By it including an others handler, it ensured that no exception
   -- will propagate out of this procedure without hitting this 'Final' code.

   -- If an exception was raised and needs to be propagated:
   if Exception_Caught /= Null_Occurrence then
      Reraise_Exception(Exception_Caught);
   end if;

end Do_Something;