Re: [boost] boost::noncopyable errors are difficult to diagnose on MSVC

Subject: Re: [boost] boost::noncopyable errors are difficult to diagnose on MSVC
From: Beman Dawes (bdawes_at_[hidden])
Date: 2009-11-06 17:13:17

On Fri, Nov 6, 2009 at 1:17 PM, Emil Dotchevski
<emildotchevski_at_[hidden]> wrote:
> On Fri, Nov 6, 2009 at 9:44 AM, Zachary Turner <divisortheory_at_[hidden]> wrote:
>> Is there anything that can be done to improve the error messages generated
>> by the compiler when a copy fails to be made due to a boost::noncopyable?
>
> Easy cure is to spell out the private declarations for the copy
> constructor and the assignment operator "by hand". We all know that
> this spells "non-copyable".

Because of C++0x deleted functions, the idiom for noncopyable is going
to change.

    class foo {
          foo( const foo & ) = delete;
          foo & operator =( const foo & ) = delete;
          ...
    };

Maybe Boost should have a macro, say BOOST_NONCOPYABLE(T), that would
generate the above for C++0x compilers, and the following for
pre-C++0x compilers:

    class foo {
          foo( const foo & );
          foo & operator =( const foo & );
          ...
    };

What the user would actually write would be:

    class foo {
          BOOST_NONCOPYABLE(foo)
          ...
    };

Another approach would be for the user to write:

    class foo {
          foo( const foo & ) BOOST_DELETED_FUNC;
          foo & operator =( const foo & ) BOOST_DELETED_FUNC;
          ...
    };

For 0x it would generate =delete while for non-0x it would generate nothing.

--Beman