On 10/6/2010 6:22 PM, Christopher Schmidt wrote:
Joel de Guzman schrieb:
On 10/6/10 8:01 AM, Jeffrey Lee Hellrung, Jr. wrote:
On 10/05/2010 04:41 PM, Joel de Guzman wrote:
On 10/6/10 5:32 AM, Jeffrey Lee Hellrung, Jr. wrote: [...]
That said, it does look the documentation for boost::fusion::for_each (indicating that F is received by value) contradicts the source code (where F is received by reference-to-const)...
Jeffrey, I don't see that here (F is received by value): http://tinyurl.com/2vdao6r. Do you?
Hmmm...that looks difference from
http://www.boost.org/doc/libs/1_44_0/libs/fusion/doc/html/fusion/algorithm/i...
Something must've changed. Christopher?
It wasn't me. In fact, the file hasn't been changed for three years:
https://svn.boost.org/trac/boost/log/trunk/boost/fusion/algorithm/iteration/...
Anyway, the functor should be passed by value. Let me quote Tobias (Schwinger) here, from an email from the 29th of October 2009 - in which he talks about passing by reference vs. passing by value in the functional subset of Fusion:
The target function is accepted by value - as the default. The functions are designed in a way that allows reference types to be used by explicitly specifying the template parameter 'Function'.
The reasons for the default were:
1. C++98-References and built-in function types do not mix well. There is a clause in the Standard rendering the program ill-formed as soon as a const qualifier gets added. There's a defect report about the issue and compiler-specific behavior may vary.
Example:
void a_func(); template< typename F> void take_func(F const&); take_func(a_func); // might or might not work
2. Consistency with existing practice, just look at the standard lib's <algorithm> header, for instance.
That makes perfect sense. In that case, the code should reflect the docs. Regards, -- Joel de Guzman http://www.boostpro.com http://spirit.sf.net