[Bug c++/51480] New: non-const default argument gets rejected

[Bug c++/51480] New: non-const default argument gets rejected

[thomas@maier-komor.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51480

             Bug #: 51480
           Summary: non-const default argument gets rejected
    Classification: Unclassified
           Product: gcc
           Version: 4.5.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: thomas@maier-komor.de


non-const default arguments get rejected with following error message:
error: default argument for 'A& a' has type 'A'

Here is an example, where function rejected causes an error, while function
accepted is accepted.

struct A
{
};

void accepted(const A &a = A())
{
}

void rejected(A &a = A())
{
}

[Bug c++/51480] non-const default argument gets rejected

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51480

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-12-09 09:34:28 UTC ---
(In reply to comment #0)
> void rejected(A &a = A())

You can't bind a non-const reference to a temporary

[Bug c++/51480] non-const default argument gets rejected

[thomas@maier-komor.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51480

--- Comment #2 from Thomas Maier-Komor <thomas@maier-komor.de> 2011-12-09 09:47:06 UTC ---
Why is that so?

Visual Studio compiler seems to handle that situation without a problem and I
think it could come handy in certain situations...

[Bug c++/51480] non-const default argument gets rejected

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51480

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-12-09 09:58:12 UTC ---
Visual Studio is not a real C++ compiler.

Try http://comeaucomputing.com/tryitout/ or http://llvm.org/demo/

Your code is not valid C++, sorry.

[Bug c++/51480] non-const default argument gets rejected

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51480

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-12-09 10:02:52 UTC ---
If you think it's useful to modify an object that will never be used, you can
do it like this:

struct A
{
};

void accepted(const A &a = A())
{
}

void rejected(A &a)
{
}

void rejected()
{
  A unused;
  rejected(unused);
}