On 29 mai, 08:36, Barry <dhb2...@gmail.comwrote:
Quote:
The problem brought by one earlier post from comp.lang.c++
http://groups.google.com/group/comp....ead/thread/bf6...
>
I take part of the question and reproduce the code to represent (partly)
the question.
>
#include <iostream>
>
template <class>
void f(...)
{
* *std::cout << "..." << std::endl;
>
}
>
template <class T>
void f(T[1])
{
* *std::cout << "T" << std::endl;
>
}
>
int main()
{
* *f<int>(0);
* *f<void>(0);
>
}
>
as "array of void" is invalid type, so the f<voidshould applies SFINAE
and chooses the "f(...)" version
>
the code above compiles and runs _expectedly_ with VC8
but fails to compile with Comuea Online, producing the error message:
>
"ComeauTest.c", line 10: error: array of void is not allowed
* *void f(T[1])
* * * * * *^
* * * * * *detected during instantiation of "f" based on template argument
* * * * * * * * * * *<voidat line 18
>
compiles with gcc 4.3.0 but produced unexpected result, producing
T
T
which means that f<int>, f<voidboth chooses the second version.
>
so who's right about this?
I guess VC8 is right.
SFINAE comes when type deduction fails, which can happen in the
following context :
14.8.2.2 :
"When an explicit template argument list is specified, the template
arguments must be compatible with the template parameter list and must
result in a valid function type as described below; otherwise type
deduction fails. Specifically, [...] Type deduction may fail for the
following reasons:
Attempting to create an array with an element type that is void"
Quote:
one more question:
should
>
8.3.5.3 [...] The type of a function is determined using the
following rules. The type of each parameter is determined from its own
decl-specifier-seq and declarator. After determining the type of each
parameter, any parameter of type array of T or function returning
T is adjusted to be pointer to T or pointer to function returning
T, respectively.
[...]
>
the adjustment apply before SFINAE happens?
I guess GCC4.3.0 gives an "yes" answer.
Such adjustement is applied after SFINAE.
14.8.2.3 :
"After this substitution is performed, the function parameter type
adjustments described in 8.3.5 are performed."
Alexandre Courpron.
