Re: [boost] [scope_exit] MSVC error C2355: 'this' : can only be referenced inside non-static member functions

26 Aug 2010

      On Wed, Aug 25, 2010 at 7:49 PM, Lorenzo Caminiti <lorcaminiti@gmail.com> wrote:
...
Hello all,
I am trying to use Boost.ScopeExit parameter binding mechanism to
implement Boost.LocalFunction. To do so, I need to use some internal
ScopeExit code to detect the type of `this` and bind its value to the
local function declaration.
The following code works on GCC but not on MSVC... This appears to be
a MSVC 2008 bug:
http://connect.microsoft.com/VisualStudio/feedback/details/331418/erroneous-...
1) Can anyone please try this code on MSVC versions later than 2008 to
see if it was fixed?
2) Do you know of a workaround for this problem?
// File: lf03.cpp
#include <boost/scope_exit.hpp>
struct c {
   void f() {
       typedef void (*this_t)(int this_ );
#if defined(BOOST_MSVC) // for MSVC
       typedef boost::type_of::msvc_typeid_wrapper<
           sizeof(*boost::type_of::encode_start(
#else // for GCC
       typedef __typeof__(
           boost::type_of::ensure_obj(
#endif
               boost::scope_exit::aux::wrap(
                   boost::scope_exit::aux::deref(
                       this, (this_t)0
                   )
               )
           )
#if defined(BOOST_MSVC) // for MSVC
       )>::type
#else // for GCC
       )
#endif
       this_w;
   }
};
int main() {
   c cc;
   cc.f();
   return 0;
}
I get this error on MSVC 2008 but the code compiles just fine on GCC:
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 14.00.50727.42 for 80x86
Copyright (C) Microsoft Corporation.  All rights reserved.
lf03.cpp
using native typeof
lf03.cpp(17) : error C2355: 'this' : can only be referenced inside
non-static member functions
lf03.cpp(22) : error C2955: 'boost::type_of::msvc_typeid_wrapper' :
use of class template requires template argument list
       C:\Program
Files\boost\boost_1_42\boost/typeof/msvc/typeof_impl.hpp(212) : see
declaration of 'boost::type_of::msvc_typeid_wrapper'
Thank you very much.
--
Lorenzo
BTW, the point of this code is to automatically determine the type of
`this`. However, all the workarounds I found of the Internet assume to
know the type `c*` of this by doing:

struct c {
    void f() {
        c& self = *this;
        ... // Use `self` instead of `this` in the type determination
code -- but I already know the type `c` since I used it above...
    }
};

so I cannot use these type of workarounds.

-- 
Lorenzo