[Boost-bugs] [Boost C++ Libraries] #3705: Boost.Function FAQ

Subject: [Boost-bugs] [Boost C++ Libraries] #3705: Boost.Function FAQ
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-12-03 08:03:44

#3705: Boost.Function FAQ
------------------------------+---------------------------------------------
 Reporter:  anonymous         |       Owner:  dgregor      
     Type:  Feature Requests  |      Status:  new          
Milestone:  Boost 1.42.0      |   Component:  Documentation
  Version:  Boost 1.41.0      |    Severity:  Problem      
 Keywords:                    |  
------------------------------+---------------------------------------------
 From
 http://groups.google.com/group/comp.lang.c++.moderated/tree/browse_frm/thread/f66ee6174fb04762/a5c99eadde5a1e52?rnum=1&_done=/group/comp.lang.c%2B%2B.moderated/browse_frm/thread/f66ee6174fb04762/a5c99eadde5a1e52%3Ftvc%3D1%26#doc_b36422ac63363172


 ---------------------------------------------------------------

 Peter Dimov
 > On Dec 2, 7:18 am, Sebastian Hauer <ha..._at_[hidden]> wrote:
 > Hi,
 > Recently I had the need for an efficient polymorphic function wrapper
 > (aka delegate), so I looked at a few possible options such as
 > boost::function and FastDelegate.  I also came across tr1::function
 > which I was blissfully unaware of until now, considering that the
 > original proposal was from late 2002
 (see:http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2002/n1402.html).
 > While reading the proposal I noticed that a tr1::function can throw a
 > bad_function_call exception if no target was assigned.
 > I was just wondering for the rationale behind this design decision.
 > In my opinion the fact that it throws goes against C++'s notion
 > of "you only pay for what you use".
 > I'm interested in hearing what your thoughts are on this.

 This behavior doesn't need to impose a cost. An std::function (it's
 officially in C++0x) that hasn't been assigned a target may internally
 store a target function that throws bad_function_call. It need not
 test on every call (even though the test wouldn't impose much overhead
 compared to the indirect call that follows.)

 -------------------------------------------------------------------

 Please add this to Boost.Function FAQ.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/3705>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.