Re: [boost] [system] virtual ~error_category

Subject: Re: [boost] [system] virtual ~error_category
From: Peter Dimov (lists_at_[hidden])
Date: 2018-02-12 20:01:33

Niall Douglas wrote:

> It's very valid for a custom error code category to allocate some sort of 
> internal state e.g. a hash table for looking up messages. This could be 
> allocated statically, but it might also be allocated by the category 
> instance on the basis that it was until now the same thing. This would not 
> be freed on destruction if the `error_category` destructor were not 
> virtual.

That's not true in the cases I can think of. Could you illustrate with code?

> But as far as Boost.System goes, I think de-virtualising its destructor is 
> a major API break.

It certainly is a potentially breaking change.

> I can see plenty of code out there in the wild relying on that destructor 
> firing when it's supposed to, and Boost devirtualising it would equal a 
> resource leak where there was none before.

Yes, it's better to make it protected, as Paul Groke observed. This way 
there'll be no silent failures.