c++/9634: Problems with templates (SFINAE)

peter schmid pschmid@peem.als.lbl.gov
Sun Feb 9 03:16:00 GMT 2003


>Number:         9634
>Category:       c++
>Synopsis:       Problems with templates (SFINAE)
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          rejects-legal
>Submitter-Id:   net
>Arrival-Date:   Sun Feb 09 03:16:01 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     Peter Schmid
>Release:        3.4 20030204 (experimental)
>Organization:
LBNL
>Environment:
System: Linux linux 2.4.19-4GB #1 Wed Nov 27 00:56:40 UTC 2002 i686 unknown
Architecture: i686
SuSE 8.1
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: ../gcc/configure --enable-threads=posix --enable-languages=c,c++,f77,objc --enable-__cxa_atexit --disable-nls
>Description:
g++ 3.4 does not accept the code taken from traits/isclasst.hpp from
>How-To-Repeat:
source code t.C

template<typename T>
class IsFunctionT {
  private:
    typedef char One;
    typedef struct { char a[2]; } Two;
    template<typename U> static One test(...);
    template<typename U> static Two test(U (*)[1]);
  public:
    enum { Yes = sizeof(IsFunctionT<T>::test<T>(0)) == 1 };
    enum { No = !Yes };
};
compiling t.C

gcc 3.4
g++ -v t.C -W -Wall
Reading specs from /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.4/specs
Configured with: ../gcc/configure --enable-threads=posix --enable-languages=c,c++,f77,objc --enable-__cxa_atexit --disable-nls
Thread model: posix
gcc version 3.4 20030204 (experimental)
 /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.4/cc1plus -quiet -v -D__GNUC__=3 -D__GNUC_MINOR__=4 -D__GNUC_PATCHLEVEL__=0 -D_GNU_SOURCE t.C -D__GNUG__=3 -quiet -dumpbase t.C -auxbase t -W -Wall -version -o /tmp/ccSkY98I.s
GNU C++ version 3.4 20030204 (experimental) (i686-pc-linux-gnu)
	compiled by GNU C version 3.4 20030204 (experimental).
ignoring nonexistent directory "NONE/include"
ignoring nonexistent directory "/usr/local/i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include/c++/3.4
 /usr/local/include/c++/3.4/i686-pc-linux-gnu
 /usr/local/include/c++/3.4/backward
 /usr/local/include
 /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.4/include
 /usr/include
End of search list.
t.C:9: error: expected primary-expression
t.C:2: warning: all member functions in class `IsFunctionT<T>' are private

gcc 3.2
/usr/bin/g++ -v t.C -W -Wall
Reading specs from /usr/lib/gcc-lib/i486-suse-linux/3.2/specs
Configured with: ../configure --enable-threads=posix --prefix=/usr --with-local-prefix=/usr/local --infodir=/usr/share/info --mandir=/usr/share/man --libdir=/usr/lib --enable-languages=c,c++,f77,objc,java,ada --enable-libgcj --with-gxx-include-dir=/usr/include/g++ --with-slibdir=/lib --with-system-zlib --enable-shared --enable-__cxa_atexit i486-suse-linux
Thread model: posix
gcc version 3.2
 /usr/lib/gcc-lib/i486-suse-linux/3.2/cc1plus -v -D__GNUC__=3 -D__GNUC_MINOR__=2 -D__GNUC_PATCHLEVEL__=0 -D__GXX_ABI_VERSION=102 -D__ELF__ -Dunix -D__gnu_linux__ -Dlinux -D__ELF__ -D__unix__ -D__gnu_linux__ -D__linux__ -D__unix -D__linux -Asystem=posix -D__NO_INLINE__ -D__STDC_HOSTED__=1 -D_GNU_SOURCE -Acpu=i386 -Amachine=i386 -Di386 -D__i386 -D__i386__ -D__tune_i486__ t.C -D__GNUG__=3 -D__DEPRECATED -D__EXCEPTIONS -quiet -dumpbase t.C -W -Wall -version -o /tmp/cctz9rQi.s
GNU CPP version 3.2 (cpplib) (i386 Linux/ELF)
GNU C++ version 3.2 (i486-suse-linux)
	compiled by GNU C version 3.2.
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/g++
 /usr/include/g++/i486-suse-linux
 /usr/include/g++/backward
 /usr/local/include
 /usr/lib/gcc-lib/i486-suse-linux/3.2/include
 /usr/i486-suse-linux/include
 /usr/include
End of search list.
t.C:2: warning: all member functions in class `IsFunctionT<T>' are private
 /usr/lib/gcc-lib/i486-suse-linux/3.2/../../../../i486-suse-linux/bin/as -V -Qy -o /tmp/ccfqXMMs.o /tmp/cctz9rQi.s
GNU assembler version 2.12.90.0.15 (i486-suse-linux) using BFD version 2.12.90.0.15 20020717 (SuSE)
 /usr/lib/gcc-lib/i486-suse-linux/3.2/collect2 --eh-frame-hdr -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 /usr/lib/gcc-lib/i486-suse-linux/3.2/../../../crt1.o /usr/lib/gcc-lib/i486-suse-linux/3.2/../../../crti.o /usr/lib/gcc-lib/i486-suse-linux/3.2/crtbegin.o -L/usr/lib/gcc-lib/i486-suse-linux/3.2 -L/usr/lib/gcc-lib/i486-suse-linux/3.2/../../../../i486-suse-linux/lib -L/usr/lib/gcc-lib/i486-suse-linux/3.2/../../.. /tmp/ccfqXMMs.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc-lib/i486-suse-linux/3.2/crtend.o /usr/lib/gcc-lib/i486-suse-linux/3.2/../../../crtn.o
/usr/lib/gcc-lib/i486-suse-linux/3.2/../../../crt1.o: In function `_start':
/usr/lib/gcc-lib/i486-suse-linux/3.2/../../../crt1.o(.text+0x18): undefined reference to `main'
collect2: ld returned 1 exit status
>Fix:
	
>Release-Note:
>Audit-Trail:
>Unformatted:
 >the book C++ templates by Vandevoorde and Josuttis. gcc 3.2 accepts
 >this code. I believe this a regression.



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