Re: I can not compile code from <<modern c++ design>>

[Di Yang <diy at qualcomm dot com>]

At 13:02 4/7/2003 +0200, Matthias Oltmanns wrote:
> Am Mon, 2003-04-07 um 11.24 schrieb Di Yang:
> > Hi,
> >
> > public:
> > enum { exists = sizeof(Test(MakeT())) == sizeof(Small) };
>
> Hi,
>
> this seems to be not valid C++ code because the calls to the
> static members 'Test' and 'MakeT' are not const expressions at compile
> time.
> For assignments to enum literals there are only integer expressions
> allowed which are evaluated at compile time.
>
> cu
> Matthias

Thank you, I changed the code as following and passed GCC 3.2:  -Di

        template <class T, class U>
        struct ConversionHelper
        {
            typedef char Small;
            struct Big { char dummy[2]; };
            static Big   Test(...);
            static Small Test(U);
            static T MakeT();
        };

    template <class T, class U>
    struct Conversion
    {
        typedef ConversionHelper<T, U> H;
        enum { exists = sizeof(typename H::Small) == 
sizeof(H::Test(H::MakeT())) };

    };
......


C:\ttt>g++ -o template template.cpp
template.cpp: In instantiation of `Conversion<double, int>':
template.cpp:40:   instantiated from here
template.cpp:40: warning: passing `double' for argument 1 of `static char
   ConversionHelper<T, U>::Test(U) [with T = double, U = int]'

C:\ttt>template
1 0
C:\ttt>

> --
> Matthias Oltmanns
>
> Tel: 04421-1543-274
> mail: Mathias dot Oltmanns dot Oltmanns at sysde dot eads dot net