Boost C++ Libraries: Ticket #1076: compile error: disconnecting struct with operator()() doesn't work in VS2005 SP1

attachment set

boris@… — Wed, 04 Jul 2007 04:49:20 GMT

attachment → testcase.cpp

owner set

Eric Niebler — Wed, 11 Jul 2007 01:51:44 GMT

owner set to doug_gregor

boris@… — Thu, 24 Apr 2008 15:13:51 GMT

The problem can also be reproduced with VC++ 9.0. Upgrading the compiler won't help unfortunately.

owner changed

Douglas Gregor — Tue, 29 Apr 2008 18:30:42 GMT

owner changed from doug_gregor to Douglas Gregor

status changed; resolution set

anonymous — Mon, 30 Nov 2009 14:19:54 GMT

status new → closed
resolution → invalid

I think you need an equality comparison here - otherwise, how will the compiler know which slot to disconnect?

struct event_handler
{
       void operator()() {}
       bool operator == ( const event_handler &rhs ) { return true; }
};

I'll see about getting the documentation updated, too.

Marshall Clow — Mon, 30 Nov 2009 14:22:20 GMT

I was the one who closed the bug.

status changed; cc set; resolution deleted

Wed, 21 Apr 2010 16:22:38 GMT

cc MartinNvPyle@… added
status closed → reopened
resolution invalid

In:

http://lists.boost.org/boost-users/2007/07/29153.php

Boris showed some error output. That seems to show his original problem with signal::disconnect was while using boost::function, not a hand crafted struct/functor as is shown here. I think he may have over simplified his example.

I have the same problem Boris had. Using VS2005, and a boost::function object I get operator==() cant be found errors when calling signal::disconnect. Of course, boost::function does have an operator==().

Here's an example:

#include <boost/signal.hpp>
#include <boost/function.hpp>
void foo()
{
}
void TrySignalDisconnect()
{
	typedef boost::function<void()> MyFunctorType;
	MyFunctorType myFunctorFoo(&foo);
	assert( &foo == myFunctorFoo ); //compiles!
	//assert( myFunctorFoo == myFunctorFoo) ); //will NOT compile
	boost::signal<void()> sig;
	sig.connect(myFunctorFoo);
	//sig.disconnect(myFunctorFoo);	//will NOT compile -- same reason
}

To me it looks like boost::function will compare with a raw function pointer, but not another boost::function ?

I hope this isn't bending the meaning of this bug too far. I'm using boost 1.35.

bschaeling — Wed, 21 Apr 2010 16:39:19 GMT

It's such a long time ago that I reported the bug that I don't remember all the details anymore. However I think your code fails because comparing boost::function objects with == and != isn't supported - see http://www.boost.org/doc/libs/1_42_0/doc/html/function/faq.html#id877361.

Thu, 22 Apr 2010 09:19:20 GMT

Thanks for the info Boris. Yes that seems to be highly relevant. I now see that lack of myFunctorFoo == myFunctorFoo support (in the above example) follows from type-erasure, plus no compile time type-trait for has operator==(T,T).

On the off chance; I don't suppose you can make sense of the (to me) cryptic statement at the end of that FAQ item: "The Signals library has a way around this" ?

status changed; resolution set

Marshall Clow — Tue, 18 Jun 2013 16:58:34 GMT

status reopened → closed
resolution → wontfix

Boost.Signals is being deprecated. Please transition to Boost.Signals2