Boost.Function FAQ

[anonymous]

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

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Peter Dimov

On Dec 2, 7:18 am, Sebastian Hauer <ha...@…> 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.)

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Please add this to Boost.Function FAQ.

[Steven Watanabe]

I don't think that this would be a good idea to add to the FAQ, given that boost::function does not work this way.