[cfe-dev] clang and a class with non-copyable and non-assignable member

[David Blaikie]

On Sat, Jan 17, 2015 at 10:59 AM, Edward Diener <
eldlistmailingz at tropicsoft.com> wrote:

> On 1/17/2015 11:53 AM, David Blaikie wrote:
>
>> Do you have a complete (standalone - preprocessed) example of this
>> behavior?
>>
>
> Currently it come from trying to build Boost.Test on Windows using clang
> for Windows built for mingw/gcc-4.8.1.
>
> There is an execution_monitor class in execution_monitor.hpp which has as
> a member:
>
> boost::scoped_ptr<detail::translate_exception_base> m_custom_translators;
>
> The detail::translate_exception_base class, which is an abstract class,
> itself has as a member:
>
> boost::scoped_ptr<translate_exception_base> m_next;
>
> boost::scoped_ptr is the inspiration for std::unique_ptr and is
> non-copyable, non-asignable. An execution_monitor instance is never copied
> or assigned.
>
> Building Boost.Test with clang gives errors:
>
> -------------------------------------------------
>
> "..\..\..\boost/test/execution_monitor.hpp:59:23: error: 'operator=' is a
> private member of 'boost::scoped_ptr<boost::detail::translate_exception_
> base>'
> class BOOST_TEST_DECL translate_exception_base {
>                       ^
> ..\..\..\boost/smart_ptr/scoped_ptr.hpp:48:18: note: declared private here
>     scoped_ptr & operator=(scoped_ptr const &);
>                  ^
> ..\..\..\boost/test/execution_monitor.hpp:59:23: note: implicit copy
> assignment operator for 'boost::detail::translate_exception_base' first
> required here
> class BOOST_TEST_DECL translate_exception_base {
>                       ^
> ..\..\..\boost/test/execution_monitor.hpp:59:23: error: field of type
> 'boost::scoped_ptr<translate_exception_base>' has private copy constructor
> class BOOST_TEST_DECL translate_exception_base {
>                       ^
> ..\..\..\boost/smart_ptr/scoped_ptr.hpp:47:5: note: declared private here
>     scoped_ptr(scoped_ptr const &);
>     ^
> ..\..\..\boost/test/execution_monitor.hpp:59:23: note: implicit copy
> constructor for 'boost::detail::translate_exception_base' first required
> here
> class BOOST_TEST_DECL translate_exception_base {
>                       ^
> ..\..\..\boost/test/execution_monitor.hpp:143:23: error: field of type
> 'boost::scoped_ptr<detail::translate_exception_base>' has private copy
> constructor
> class BOOST_TEST_DECL execution_monitor {
>                       ^
> ..\..\..\boost/smart_ptr/scoped_ptr.hpp:47:5: note: declared private here
>     scoped_ptr(scoped_ptr const &);
>     ^"
>
> ----------------------------------------------
>
> Gcc 4.8.1, which is used to build clang has no problem with any of this.
>
> I can try to work up as simple a standalone example as possible which will
> replicate this behavior.
>

Step one is just to get the preprocessed source (compile with -E) and check
that that reproduces the behavior - you can at least share that with us
then we won't have to try to get exactly the same version of boost,
whatever other system headers you have, etc.

(though it might still be something that only reproduces in windows mode,
so knowing the full underlying command line (if you're running clang
manually, you can run with -### and give us the details it prints out) can
be useful too)

Ah, I think I see what it is (perhaps we could do a better job of the
diagnostic)

BOOST_TEST_DECL can expand to declspec(dllexport) (
http://www.boost.org/doc/libs/1_40_0/boost/test/detail/config.hpp ) - which
would (perhaps only on Clang?) cause all the implicit special members, like
assignment operators, to be generated. Since it can't be generated, it
fails.

Maybe the right behavior here is to only generate those that are valid?
(one of the Windows-y guys (cc'd) will probably test out the various corner
cases with MSVC here and see what the desired behavior is)


>
>
>> On Sat, Jan 17, 2015 at 8:06 AM, Edward Diener
>> <eldlistmailingz at tropicsoft.com
>> <mailto:eldlistmailingz at tropicsoft.com>> wrote:
>>
>>     I am using the latest clang built from source. I am seeing this
>>     situation:
>>
>>     class XXX { some_non_copyable_non___assignable_member_type member; }
>>
>>     An object of class XXX never gets copied or assigned (it's a
>>     singleton ) and yet clang is giving an errors of the form:
>>
>>     error: 'operator=' is a private member of
>>     'some_non_assignable_member___type'.
>>
>>     and
>>
>>     error: field of type
>>     'some_non_copyable_non___assignable_member_type' has private copy
>>     constructor
>>
>>     My understanding of C++ is that if a member of a class is
>>     non-copyable and non-assignable and an instance of that class is
>>     never copied or assigned it is not an error even if the compiler
>>     would be creating a default copy constructor and default assignment
>>     operator when the class does not have user-defined versions.
>>
>>     The command line options to the clang++.exe compiler are:
>>
>>     -c -x c++ -O0 -g -fno-inline -Wall -pedantic -g
>>
>>
>>
>>
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>>
>>
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