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I don't think I understand, you can throw from a destructor. However, in C++11 it gets tricky because destructors are implicitly declared noexcept, so if you w

I don't think I understand, you can throw from a destructor. However, in C++11 it gets tricky because destructors are implicitly declared noexcept, so if you want to do so you need to mark them noexcept(false). As for implementing scope(exit) yeah, apparently this isn't possible.

mehrdadn 9y ago
> I don't think I understand, you can throw from a destructor Read what I wrote carefully: >> destructors invoked via exceptions can't throw their own exceptions i.e. if you are in a block where an exception is thrown, and a destructor is called during the exception's propagation, then that destructor cannot throw its own exception, as it will terminate the program. (This is unrelated to noexcept.) See here for more info: https://stackoverflow.com/a/130123 https://stackoverflow.com/a/130123
- beached_whale 9y ago
  Ah I see, like struct B { ~B( ) noexcept( false ) { throw ...; } }; struct A { B b; ~A( ) noexcept( false ) { throw...;} }; I guess the saving grace is that most C++ devs are aware of what could throw in a destructor because it is rare and C++ 11 made this more difficult. Just don't and design around it. If the destructor fails use it as a choice to terminate or ignore.
  - mehrdadn 9y ago
    Yeah. But when people start writing wrappers like SCOPE_EXIT that call user code inside destructors, suddenly the users of those wrappers don't have any way to know they can't throw exceptions.
    - beached_whale 9y ago
      scope_exit is just not very idiomatic C++. If used, It's for quick'n'dirty I'm too rushed to wrap it in a class times. It's use in C++ implies that you are worrying about something at the wrong abstraction level too. With that though, I would think that the default > c++11 implicit noexcept is proper. Crash hard when an exception is thrown and maybe even static assert on the result of noexcept( on_exit_cb ) so that it gives a compile error, lambda's can be noexcept and c functions cannot throw(thinking fclose and friends)
    - maxlybbert 9y ago
      The people who use SCOPE_EXIT are responsible for making sure no exceptions are thrown (well, that any exceptions that get thrown are swallowed before they trigger std::terminate). If that’s not possible, they have to use a different approach.

mehrdadn 9y ago

> I don't think I understand, you can throw from a destructor Read what I wrote carefully: >> destructors invoked via exceptions can't throw their own exceptions i.e. if you are in a block where an exception is thrown, and a destructor is called during the exception's propagation, then that destructor cannot throw its own exception, as it will terminate the program. (This is unrelated to noexcept.) See here for more info: https://stackoverflow.com/a/130123 https://stackoverflow.com/a/130123

beached_whale 9y ago
Ah I see, like struct B { ~B( ) noexcept( false ) { throw ...; } }; struct A { B b; ~A( ) noexcept( false ) { throw...;} }; I guess the saving grace is that most C++ devs are aware of what could throw in a destructor because it is rare and C++ 11 made this more difficult. Just don't and design around it. If the destructor fails use it as a choice to terminate or ignore.
- mehrdadn 9y ago
  Yeah. But when people start writing wrappers like SCOPE_EXIT that call user code inside destructors, suddenly the users of those wrappers don't have any way to know they can't throw exceptions.
  - beached_whale 9y ago
    scope_exit is just not very idiomatic C++. If used, It's for quick'n'dirty I'm too rushed to wrap it in a class times. It's use in C++ implies that you are worrying about something at the wrong abstraction level too. With that though, I would think that the default > c++11 implicit noexcept is proper. Crash hard when an exception is thrown and maybe even static assert on the result of noexcept( on_exit_cb ) so that it gives a compile error, lambda's can be noexcept and c functions cannot throw(thinking fclose and friends)
  - maxlybbert 9y ago
    The people who use SCOPE_EXIT are responsible for making sure no exceptions are thrown (well, that any exceptions that get thrown are swallowed before they trigger std::terminate). If that’s not possible, they have to use a different approach.