Re: Question about 14.3.1 - template arguments without linkage
Gary McNickle ha scritto:
The standard states that "A type without linkage shall not be used as a
template-argument for a template type-parameter".
I believe I understand why this restriction is in place, and generally
agree with it - but I have discovered that the compiler that I am using
ignores this restriction, and I am trying to understand the implications.
Please consider the following example code;
void foo()
{
std::vector<int> ints;
// populate ints...
struct SortPredicate : public std::binary_function<int,int,bool>
{
bool operator()(int lhs,int rhs)
{
return (lhs<rhs);
}
};
std::sort(ints.begin(), ints.end(), SortPredicate());
}
Does the fact that the SortPredicate does not have any linkage pose any
potential stability issues or undefined behavior in the code, at least
when used in this manner? If so, does the same hold true if the type
were not a POD type?
The code is currently ill-formed and should be rejected by the compiler.
The POD-ness of the type is irrelevant. However, the issue is under
revision from the CWG (see paper
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2402.pdf) and a
few compilers are known to implement the proposed relaxed rules as an
extension. In case the proposal is accepted (which appears to be very
likely) you will have to wait for C++0x to be standardized before you
can declare you code as "portable".
HTH,
Ganesh
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