Re: [Boost-users] How to use noncopyable?

Subject: Re: [Boost-users] How to use noncopyable?
From: Kim Barrett (kab.conundrums_at_[hidden])
Date: 2009-02-22 02:34:23

At 2:12 AM -0500 2/22/09, Yang Zhang wrote:
>>Yang Zhang wrote:
>>>Hi, I can't figure out how to properly use noncopyable.  I'm always
>>>getting things like "has a non-virtual destructor" warnings.
>>
>>Do you have a simple test case?
>
>$ cat noncopyable.cc
>#include <boost/noncopyable.hpp>
>using namespace boost;
>class C : noncopyable {};
>int main() { return 0; }
>
>$ g++ -Wall -g3 -o noncopyable noncopyable.cc [...] -Weffc++ [...]
>cc1plus: warnings being treated as errors
>noncopyable.cc:3: error: base class âclass 
>boost::noncopyable_::noncopyableâ has a non-virtual destructor
>
>I understand that this shouldn't be a problem as noncopyable is not 
>meant to be used directly as any variable's static type, but I do 
>require enabling this warning.

The warning is due to the use of -Weffc++:

   Warn about violations of the following style guidelines from Scott Meyers'
   Effective C++ book:

     ...
     * Item 14: Make destructors virtual in base classes.
     ...

This is a case where that admonition is wrong. (It is a style guideline
after all, and not necessarily prescriptive.) You might be able to suppress
this warning by using -Wno-nonvirtual-dtors, but that may suppress warnings
that you would actually like to see. This is one of the reasons why we're
not using -Weffc++ where I work. (I think I recall there being some boost
libraries that run afoul of item 7 "Never overload &&, ||, or ,." too.)