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Arne Adams
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 Posted: Sat Dec 10, 2005 1:06 pm Post subject: deduced Parameter does not match |
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template<class Parameter, class Host> void Configure(Parameter, void
(Host::*)(Parameter))
{/* do something useful*/}
// something did not match - generate a compiler error that might clarify
what went wrong
template<class Parameter, class MemFun> void Configure(Parameter p, MemFun
f)
{
CheckParameter(p,f);
}
struct
ERROR_ERROR_ERROR_the_type_of_the_parameter_for_your_member_function_does_not_match_the_first_parameter_of_Configure_ERROR_ERROR_END;
template<class WrongParameter, class NeededParameter, class Host>
void CheckParameter(WrongParameter, void (Host::*)(NeededParameter))
{
ERROR_ERROR_ERROR_the_type_of_the_parameter_for_your_member_function_does_not_match_the_first_parameter_of_Configure_ERROR_ERROR_END
dontCompileThis;
}
struct Horst
{
void Fifi(Horst&);
};
int main(int argc, char* arg[])
{
Horst horst;
Configure(horst,&Horst::Fifi);/* Compiler error mentioning
ERROR_ERROR_ERROR_the_type_of_the_parameter_for_your_member_function_does_not_match_the_first_parameter_of_Configure_ERROR_ERROR_END;*/
return 0;
}
Both GCC 3.3 and MSVC++ 7.1 seem to agree here - the problem goes away when
Fifi does accept Horst per copy and as well when Configure<Horst&> is
called.
Why is Parameter not deduced as Host& here - is this behaviour conforming?
Kind Regards,
Arne
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]
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benben
Guest
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| Posted: Sun Dec 11, 2005 12:58 pm Post subject: Re: deduced Parameter does not match |
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| Quote: | [demostration code snipped]
Both GCC 3.3 and MSVC++ 7.1 seem to agree here - the problem goes away when
Fifi does accept Horst per copy and as well when Configure<Horst&> is
called.
Why is Parameter not deduced as Host& here - is this behaviour conforming?
|
Because
void Host: *)(Parameter)
and
void Host:*)(Parameter&)
are different types. Allowing they to be treated as the same type will
have a subtle effect where discriminating reference type does matter.
To work around you can do the following:
// start with some helper templates:
template <typename T> struct get_base_type{
typedef T type;
};
tempatle <typename T> struct get_base_type<get_base_type
typedef T type;
};
class Yes{}; class No{};
template <typename T1, typename T2> struct is_same_type{
typedef No result;
};
template <typename T> struct is_same_type<T, T>{
typedef Yes result;
};
template <typename T> struct static_assert{
typedef typename T::ERROR_ERROR_BLAH_BLAH_BLAH error;
typedef No type;
};
template <> struct static_assert<Yes>{
typedef Yes type;
};
// then the function template:
template<class Param1, class Param2, class Host>
void configure(
Param1,
void(Host::*)(Param2))
{
typedef typename get_base_type<Param2>::type P2;
typedef typename is_same_type<Param1, P2>::type R;
typedef sttic_assert<R>::type Assertion;
// ...
}
| Quote: |
Kind Regards,
Arne
|
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]
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