[Bug c++/37043] New: fails to find operator match when constructing object on the fly

[Bug c++/37043] New: fails to find operator match when constructing object on the fly

[scott at stg dot net]

Code below fails with "no match for operator>>", although works in msvc.  If
I'm doing something wrong or there is simple workaround please let me know. 
scott@stg.net.

#include <stdio.h>

class FooBar
{
public:
        FooBar(const char *s)
        {
                printf("Constructed: %s\n",s);
        }
        void Accept(const char *s)
        {
                printf("Passed: %s\n",s);
        }
};

FooBar& operator>> (const char *s,FooBar& dest)
{
        dest.Accept(s);
        return(dest);
}

int main(int argc,char **argv)
{
        FooBar test1("one");

        "A">>test1;

        "B">>FooBar("two");
}


-- 
           Summary: fails to find operator match when constructing object on
                    the fly
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: scott at stg dot net


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37043

[Bug c++/37043] fails to find operator match when constructing object on the fly

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2008-08-06 22:13 -------
You cannot bind a rvalue to a reference, only a constant reference or to a non
reference.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37043

[Bug c++/37043] fails to find operator match when constructing object on the fly

[scott at stg dot net]

------- Comment #2 from scott at stg dot net  2008-08-07 13:31 -------
Okay, so if I change:

FooBar& operator>> (const char *s,FooBar& dest)

to

FooBar operator>> (const char *s,FooBar dest)

It now compiles on both msvc and g++, but required functionality (operation
affecting existing object, not making new copy of it) is lost.

Is there some reason that using a reference to rvalue in operator>> is
disallowed in gcc and not msvc?  If so, why doesn't it fail in the A>>object;
instance where the object has already been instantiated separately?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37043

[Bug c++/37043] fails to find operator match when constructing object on the fly

[scott at stg dot net]

------- Comment #3 from scott at stg dot net  2008-08-07 13:53 -------
For clarification, this code compiles & runs in gcc & msvc:
        FooBar test1("one");
        "A">>test1;

And this code compiles & runs fine in msvc, but gives compile error in gcc:
        "B">>FooBar("two");

Since it's the same class, why should there be any difference in matching
operator>> depending on how it's instantiated?

The sample code is a distillation (demonstration) from a larger code base for
convenience of exploring this issue.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37043

[Bug c++/37043] fails to find operator match when constructing object on the fly

[schwab at suse dot de]

------- Comment #4 from schwab at suse dot de  2008-08-07 15:19 -------
Because the result of FooBar("two") is an rvalue, but test1 is an lvalue.


-- 

schwab at suse dot de changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37043