Anders Logg wrote: > On Sun, Feb 07, 2010 at 10:58:44PM +0000, Garth N. Wells wrote: >> >> Anders Logg wrote: >>> This looks a like a non-optimal solution. Are you returning the mesh >>> by value? That will lead to creation of a temporary and copying of the >>> entire refined mesh. >>> >> So they used say ;). Apparently modern compilers are all clever enough >> not to. >> >> Garth > > Is that really so? Do you have any good references that explain this > in detail?
http://en.wikipedia.org/wiki/Return_value_optimization and from 'man gcc' -fno-elide-constructors The C++ standard allows an implementation to omit creating a temporary which is only used to initialize another object of the same type. Specifying this option disables that optimization, and forces G++ to call the copy constructor in all cases. Garth This could potentially lead to many changes in DOLFIN where > we could return by value rather than by reference with the prime > example being > > A = assemble(a); > > But does it really handle non-copying of a wrapped PETSc data structure? > > -- > Anders > > >>> What if we have >>> >>> FooRefinement::refine(old_mesh, new_mesh) >>> >>> or similar? >>> >>>> ------------------------------------------------------------ >>>> revno: 4461 >>>> committer: Garth N. Wells <[email protected]> >>>> branch nick: dolfin-nompi >>>> timestamp: Sun 2010-02-07 21:53:42 +0000 >>>> message: >>>> Work on mesh refinement interface. >>>> >>>> Do not overwrite old mesh inside refinement functions belonging to >>>> static classes. Need to keep old mesh to peform update in adapative >>>> methods, so previously the mesh had to be copied before calling >>>> refine(...). >>>> modified: _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
