Re: [Boost-users] Can not compile a program that uses typeofpackage by gcc?

23 Oct 2008

      Peng Yu:
...
On Wed, Oct 22, 2008 at 9:28 PM, Steven Watanabe  
wrote:
...
AMDG
Peng Yu wrote:
...
Because of a bug in GCC, BOOST_TYPEOF (which essentially is a macro
for 'typeof') does not work for the attached code. I tried GCC 4.1.1,
somebody else tried GCC 4.3.0. Neither of them work for the attached
code.
What attached code?
Sorry, I forgot to attach the code. Here is the attached code.
This is not what Steven meant. It was probably the use of the term "traits" 
that threw you away. multiply_traits is not a traits class; it's just an 
implementation detail that places a level of indirection between typeof and 
the signature.

Wherever you need to use

BOOST_TYPEOF( T1() * T2() )

in a function signature, you replace it with

typename multiply_helper::type

where

template struct multiply_helper
{
    typedef BOOST_TYPEOF( T1() * T2() ) type;
};

Nobody specializes multiply_helper. It just moves the typeof a bit to 
satisfy the compiler.

The underlying reason for all this dance is that compilers cannot mangle an 
arbitrary expression into a function name, and typeof allows one to put 
arbitrary expressions in signatures.

--
Peter Dimov
http://www.pdplayer.com