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https://issues.apache.org/jira/browse/STDCXX-605?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Travis Vitek updated STDCXX-605:
--------------------------------
Attachment: stdcxx-605-v2.patch
stdcxx-605-v1.patch
In the failure you mention, the conversion we want is to `const int&'. The
conversion operator that gets invoked is the non-const `operator T&' with 'T'
being 'const int'. That conversion operator calls the non-const retrieve(),
which keeps the const and looks in the static dynatype::map<const int> for a
value. We should be looking in dynatype::map<int>, but the const is not being
stripped.
Consider the following...
struct S
{
private:
template <class T> int g (T*) { return 0; }
template <class T> int g (const T*) const { return 1; }
public:
template <class T> int f () { return g ((T*)0); }
};
int main ()
{
const int a = S().f<int>();
const int b = S().f<const int>();
return (a << 1) | b;
}
I believe that the expected result is 0. When compiling the S().f<const int>(),
I see a few candidate functions for overload resolution. Given that the
overload resolution system treats member functions as if they were free
functions with a correctly cv-qualified implicit object parameter, the
candidates would seem to be
int S_g(S&, int*);
int S_g(S&, const int*);
from the first template, and
int S_g(const S&, int*);
int S_g(const S&, const int*);
from the second. The actual type of the call is
??? S_g(S&, const int*);
So the best match is easily selected, and the result is a call to the non-const
'g' template, which leaves the const on the template type T instead of
stripping it like we want.
Continuing with the example, I see a few options. We could make both 'g'
overloads share the same constness. If we make them have the same constness,
then the overload resolution chooses the best match based on the explicit
parameter type, and then discards const as we want. The disadvantage of this is
that we would either have two const overloads of 'g' [which you didn't appear
to like], or we can have two non-const overloads and cast away const when
calling from a const member function. A third option would be to make both 'g'
overloads into non-member functions that takes const S* [essentially the same
as making both members const], but that would require some code rearranging.
Personally I thought that the two const retrieve() overloads was the simplest
and cleanest solution [stdcxx-605-v2.patch]. The most recent patch involves
changing fewer lines of code in the example, but it leaves a nasty static/const
cast [stdcxx-605-v1.patch].
> [IBM XLC++] errors compiling dynatype.cpp
> -----------------------------------------
>
> Key: STDCXX-605
> URL: https://issues.apache.org/jira/browse/STDCXX-605
> Project: C++ Standard Library
> Issue Type: Bug
> Components: Examples
> Affects Versions: 4.2.0
> Environment: XLC++ 6.0 through 9.0/AIX 5.3
> Reporter: Martin Sebor
> Assignee: Travis Vitek
> Fix For: 4.2.1
>
> Attachments: stdcxx-605-v1.patch, stdcxx-605-v2.patch
>
>
> The dynatype.cpp example program fails to compile with IBM XLC++ 9.0 on AIX
> with ethe following errors:
> xlCcore_r -c -I$(TOPDIR)/include/ansi -I$(TOPDIR)/include
> -I$(BUILDDIR)/include -I$(TOPDIR)/examples/include -O -Q
> -qtemplateregistry=dynatype.ti $(TOPDIR)/examples/tutorial/dynatype.cpp
> "$(TOPDIR)/examples/tutorial/dynatype.cpp", line 203.27: 1540-0216 (S) An
> expression of type "dynatype" cannot be converted to type "int".
> "$(TOPDIR)/examples/tutorial/dynatype.cpp", line 209.30: 1540-0216 (S) An
> expression of type "dynatype" cannot be converted to type "double".
> "$(TOPDIR)/examples/tutorial/dynatype.cpp", line 215.30: 1540-0216 (S) An
> expression of type "dynatype" cannot be converted to type "double".
> "$(TOPDIR)/examples/tutorial/dynatype.cpp", line 222.35: 1540-0216 (S) An
> expression of type "dynatype" cannot be converted to type "const char *".
> "$(TOPDIR)/examples/tutorial/dynatype.cpp", line 228.35: 1540-0216 (S) An
> expression of type "dynatype" cannot be converted to type "const char *".
> "$(TOPDIR)/examples/tutorial/dynatype.cpp", line 238.28: 1540-0216 (S) An
> expression of type "dynatype" cannot be converted to type "char".
> gmake: *** [dynatype.o] Error 1
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