[Bug libstdc++/56922] New: set: the default constructor should be explicit

["akim.demaille at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56922

             Bug #: 56922
           Summary: set: the default constructor should be explicit
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: akim.demaille@gmail.com


Hi all,

According to http://llvm.org/bugs/show_bug.cgi?id=15724, there is no default
constructor for set, only a constructor whose arguments are optional, but it
turns out that this constructor is explicit.  So, at least according to C++98
(I don't know about C++11), the following piece of code is expected to fail.


$ cat /tmp/set.cc
#include <set>
int
main()
{
  std::set<int> s = {};
}
$ g++-mp-4.8 -std=c++11 -Wall /tmp/set.cc

Clang rejects it.

$ clang++-mp-3.3 -std=c++11 -Wall /tmp/set.cc -stdlib=libc++
/tmp/set.cc:5:17: error: chosen constructor is explicit in copy-initialization
  std::set<int> s = {};
                ^   ~~
/opt/local/libexec/llvm-3.3/bin/../lib/c++/v1/set:378:14: note: constructor
declared here
    explicit set(const value_compare& __comp = value_compare())
             ^
1 error generated.

The actual case at hand is a function with an optional argument which is a set,
and I used "= {}", which is rejected by clang++.

Cheers!