On 2/6/2011 5:46 PM, Lorenzo Caminiti wrote:
On Sun, Feb 6, 2011 at 3:23 PM, Jeffrey Lee Hellrung, Jr. <jhellrung@ucla.edu> wrote:
On 2/6/2011 9:17 AM, Lorenzo Caminiti wrote: [...]
I am posting here the code generated by the macros which might help curious readers in spotting costly operations performed by Boost.Local (if there are any). This of course does not include the preprocessing time. (I hope it's not too much code... just try to get passed the typeof noise at the beginning...)
Is the use of Boost.Typeof optional? I.e., can I just provide the types of the arguments and bound variables myself?
No but I think you can simply use a normal (not bound) local function parameters to do this: [...]
So Boost.Typeof is necessary to bind variables...? [...]
boost::scope_exit::aux::declared< boost::scope_exit::aux::resolve< sizeof(boost_local_auxXargs)>::cmp1<0>::cmp2> boost_local_auxXargs;
Shouldn't the name boost_local_auxXargs have some kind of line number or counter or function name pasted into it to prevent name collision of multiple BOOST_LOCAL_FUNCTION declarations in the same scope?
No, this has to be a global extern variable declared as:
extern boost::scope_exit::aux::undeclared boost_local_auxXargs;
in one of Boost.Local headers. It's a trick carried over 100% from Boost.ScopeExit (as I understand it, this is because only global or static variables can be used from within a nested block http://lists.boost.org/Archives/boost/2006/11/113658.php).
Ugh, okay ;) Will read the link. [...]
For maintenance purposes, do you plan on providing a brief sketch of the above mechanism (e.g., the main players in the above macro expansion, and the inheritance from function_base and type-erasure to simulate the binding of local functions to template parameters)?
Yes, I can add an Appendix with the pseudo code in the library docs.
Excellent.
I remember you doing an earlier study on the performance impact of using this type erasure (compared to moving the local function to namespace scope and avoid the overhead of the virtual dispatch)...is that included in the documentation? I don't see it from a quick glance...
A preliminary study was hinted by John Bytheway (http://lists.boost.org/Archives/boost/2010/09/170891.php). I have not done any performance study of Boost.Local yet (yes, I will include performance considerations in the docs once I do them).
This must be what I remembered. - Jeff