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Re: Your C++ Wish List (Editorial)
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Posted: Sep 28, 2004 4:58 AM
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I like templates and use them frequently and the most libraries are based on them too, but what I miss is the possibility to define templates with an unknown number of parameters.
The BOOST tuple class or signal/slot classes or many others use copy & paste (or the preprocessor) and they are all limited to a fixed maximal count of parameters (e.g. 3 or 5 or 10).
It would be nice, if C++ could itself construct templates with any number of parameters (as '...' in printf()).
extensions to C++:
- '...' in templates
- '##' is the number of '...' parameters (N)
- '#' iterates over all the parameters (1 - N)
examples:
template<class A, ...> class X
{
typedef # arg#_type;
X(A a, ...) { }
};
template<class T, ...> f(const T& t, ...)
{
g(t, ...);
}
template<typename F, typename T, ...>
class result_of<F(...)>
{
static F f;
static # t#;
public:
typedef typeof(f(...)) type;
};
template <...>
struct group
{
# a#;
group(...)
: a#(#...)
{}
};
template <class Ch, class Tr, ...>
inline
BOOST_IO_STD basic_ostream<Ch, Tr>&
operator << (BOOST_IO_STD basic_ostream<Ch, Tr>& os,
const group<...>& x)
{
os << x.a#;
return os;
}
I know this is hard work for compiler vendors but this would replace many copy & paste code and fewer use of the preprocessor.
I would also appreciate, if the header guards (with "#ifdef") could be replaced by another command
(e.g. "#pragma once" like some (but not all) vendors do - I know that this is another pp-command, but easier to use).
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