Re: [Boost-users] [type_traits] will the future has_operator_left_shift be able to test if a type is serializable to a stream ?

2 Feb 2011

      On 02/02/2011 08:23, Frédéric Bron wrote:
...
Could it be a problem of line ending (windows/linux)? Could you try
with that version:
http://www.boostpro.com/vault/index.php?action=downloadfile&filename=type_traits-dos.tar.bz2&directory=Extension&
I just tried and it gives the same error.

Actually it seems MSVC doesn't like "not", "or" and "and" : replacing 
them with "!", "||" and "&&" makes the error (and the warning) go away.

However next, the following code :
     BOOST_STATIC_ASSERT(( boost::has_operator_left_shift< int, int
...
::value ));
Yields the rather non-informative error :
..... the code ..... : error C4430: missing type specifier - int 
assumed. Note: C++ does not support default-int
(yes that's the only line in the error trace...)

And :
     BOOST_STATIC_ASSERT(( boost::has_operator_left_shift< std::ostream, 
int >::value ));

Adds a warning on top of the same error :

boost/type_traits/detail/has_binary_operator.hpp(106) : warning C4913: 
user defined binary operator ',' exists but no overload could convert 
all operands, default built-in binary operator ',' used
         boost/type_traits/detail/has_binary_operator.hpp(142) : see 
reference to class template instantiation 
'boost::detail::has_operator_left_shift_impl::has_operator_left_shift_impl' 
being compiled
         with
         [
             LHS=std::ostream,
             RHS=int,
             RET=void
         ]
         ..... the code ..... : see reference to class template 
instantiation 'boost::has_operator_left_shift' being compiled
         with
         [
             LHS=std::ostream,
             RHS=int
         ]
..... the code ..... : error C4430: missing type specifier - int 
assumed. Note: C++ does not support default-int

I will try and have another look later today, do you have any idea where 
the problem might be ?
...
...
However it doesn't work with a pointer type, for instance this fails :
    BOOST_STATIC_ASSERT(( boost::has_operator_left_shift<  std::ostream, void*::value ));
Can you say what you mean by it doesn't work? Do you mean compile
error or returns the wrong value?
Sorry, I meant the assertion fails.

Another case which doesn't compile however is :

     struct convertible_ambiguous
     {
         operator int() const;
         operator float() const;
     };
     BOOST_STATIC_ASSERT(( boost::has_operator_left_shift< std::ostream, 
convertible_ambiguous >::value ));

Thanks !
MAT.

Re: [Boost-users] [type_traits] will the future has_operator_left_shift be able to test if a type is serializable to a stream ?

Mathieu Champlon