问题描述
Java具有finalize块，该块允许在剩下
块之后执行一些语句（即使引发异常也被执行）。例如：
Java has the finalize block which allows to execute some statements after a blockis left (executed even if an exception is raised). Example:
try {
...
} catch (Exception e) {
...
} finally {
... // any code here
}
Ada具有可实现 Finalize 操作
的受控对象，但是没有与Java中等效的finalize块。这对于日志记录，
关闭文件，事务等（无需为每个可能的块创建特定的标记类型）很有用。
Ada has the controlled objects which allows to implement a Finalize operationbut there is no finalize block equivalent as in java. This is useful for logging,closing files, transactions and so on (without having to create a specific tagged type for each possible block).
- 您如何在Ada 2005中实现这样的finalize块（同时保持代码可读性？）？
- Ada 2012中是否有计划允许轻松执行任何finalization代码？
推荐答案
我相信这段代码将满足您的要求；它会成功打印出 42 并显示当前的收入或返回返回。
I believe this code will do what you ask; it successfully prints out 42 with the present raise or with return. It's an implementation of T.E.D's suggestion.
在Mac OS X，Darwin 10.6.0上使用GCC 4.5.0进行了测试。
Tested with GCC 4.5.0 on Mac OS X, Darwin 10.6.0.
with Ada.Finalization;
package Finally is
-- Calls Callee on deletion.
type Caller (Callee : not null access procedure)
is new Ada.Finalization.Limited_Controlled with private;
private
type Caller (Callee : not null access procedure)
is new Ada.Finalization.Limited_Controlled with null record;
procedure Finalize (Object : in out Caller);
end Finally;
package body Finally is
procedure Finalize (Object : in out Caller)
is
begin
Object.Callee.all;
end Finalize;
end Finally;
with Ada.Text_IO; use Ada.Text_IO;
with Finally;
procedure Finally_Demo is
begin
declare
X : Integer := 21;
-- The cleanup procedure, to be executed when this block is left
procedure F
is
begin
Put_Line ("X is " & Integer'Image (X));
end F;
-- The controlled object, whose deletion will execute F
F_Caller : Finally.Caller (F'Access);
begin
X := 42;
raise Constraint_Error;
end;
end Finally_Demo;
这篇关于在Ada（2005或2012）中实现等效于Java finalize块的最佳实践的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！