}
static alpha_type to_alpha(const value_type&)
{
BOOST_STATIC_ASSERT(false);
}
static value_type from_alpha(const alpha_type&)
{
BOOST_STATIC_ASSERT(false);
}
};
struct basic_composition_tag;
}
struct alpha_
{
typedef int alpha_type;
typedef char value_type;
char from_alpha(const alpha_type& x)
{
return 0;
}
int to_alpha(const value_type& x)
{
return 0;
}
};
int main(void)
{
typedef beta::composition_base<alpha_> a;
sizeof(a);
return 0;
}
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
on msvc(Version 9.0) and gcc 4.3.3.
Behavior:-
a) msvc -- compiles well
b) gcc -- throws error, basically assert failure
Even when I write,
int main(void)
{
//typedef beta::composition_base<alpha_> a;
//sizeof(a);
return 0;
}
The conclusion: don't use microsoft crap
The behavior is same.
$1. Is there any problem in BOOST_STATIC_ASSERT ? I will ask in boost
forum for it. Or else you know then please answer it.
No, it works fine.
$2. Why gcc is complaining error even when template instantiation has
not been done ? (second case)
Because the compilation fails. And it fails because you are doing this:
BOOST_STATIC_ASSERT( false );
in your code.
$3. I understand that any direct use of compositon_base::{to/from }
_alpha is bound to cause problem. But if any code is not touching it,
in that case why compiler is throwing error.
Have you checked the BOOST_STATIC_ASSERT source code and the reference
manual? It is checking statically during the compilation whether it
passed or not. For example:
BOOST_STATIC_ASSERT( 4 == sizeof( int ) );
on some systems this will fail
$4. When does static function definition gets instantiated ? If in a
compilation unit, presence of a static function name and definition
anywhere (inside class or outside class) causes it to get instantiated
also, then does the gcc compiler is checking extra for a possible
error in instantiation of a composition_base class.
The use of BOOST_STATIC_ASSERT() is to statically check something during
the compilation.
Thanks Vladimir. I just read documentation of BOOST_STATIC_ASSERT,
http://www.boost.org/doc/libs/1_39_0/doc/html/boost_staticassert.html.
And looked into the section:- "Use in templates". Looks like this
behavior is more related to gcc. But I will not wish to call msvc