benn/lumiera_
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Research: gotcha!

Browse source 
the alledged compiler error turned out to be
just plain flat lack of attention on my side.

I forgot to revert an previous experimental change:
The "wrapper" in the factory takes the argument by-value
(I forgot to add he && back in, which I removed while
fighting with other compilation problems)
This commit is contained in:
Fischlurch 2014-09-22 01:16:46 +02:00
parent e676eb6da8
commit 6fa8b41e1d
1 changed files with 17 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

22
research/try.cpp
View file

@ -31,7 +31,16 @@
/** @file try.cpp
** Investigation: pitfalls of "perfect forwarding".
** Find out about the corner cases where chained argument forwarding
** does not work as expected
** does not work as expected. The key point is to put close attention on the
** template parameters we're passing on to the next lower layer. It is crucial
** either to add the reference explicitly, or to have it included implicitly
** by relying on the way how template params are matched on function calls:
** - lvalue -> parameter becomes TY &
** - rvalue -> parameter becomes TY
**
** In this final stage, the example shows what happens if we erroneously fail
** to take the variadic arguments by '&&' on forwarding: we end-up with a
** slicing copy to the base class.
**
*/
@ -62,7 +71,10 @@ class Interface
virtual ~Interface() { }
virtual string op() const =0;
virtual string op() const
{
return "happy SLICING";
}
};
class Impl
@ -122,10 +134,10 @@ invoke (Interface const& ref)
template<class FUN, typename...ARG>
void
indirect_1 (FUN fun, ARG&&... args)
indirect_1 (FUN fun, ARG... args) // NOTE: erroneously taking ARG as-is, which results in taking BY VALUE when used in the forwarding chain!
{
diagnostics<ARG&&...> ("Indirect-1", args...);
fun (std::forward<ARG> (args)...);
diagnostics<ARG...> ("Indirect-1", args...);
fun (args...);
}
template<class FUN, typename...ARG>