On Thu, Apr 22, 2010 at 11:43 AM, Robert Jones
I'm not able to use the latest Boost release, so I've plagarised some little bits that are useful, and in the process might have missed something, so bear with me.
I have this bit of code...
#include <algorithm> #include
template < class SinglePassRange, class UnaryFunction > UnaryFunction for_each( SinglePassRange & rng, UnaryFunction fun ) { return std::for_each( boost::begin( rng ), boost::end( rng ), fun ); }
struct A { }; void f( const A & );
std::vector< A > generateVec( );
int main( ) { for_each( generateVec( ), f ); }
which understandably fails to compile as I'm passing an lvalue as non-const reference. I can fix this by adding a const ref overload of for_each, but no such overload exists in the real boost range header (AFAIK).
Gosh this was unfortunate. The lack of a const overload existed only on the trunk (never the release branch) for a few days. This could not have been more wrong if I coloured it purple! You should indeed match the current trunk and the release branch by adding a const overload for_each.
Returning containers by value seems to be the 'right way' now, as RVO should sort out the copy elision.
I'm not convinced that this is the 'right way'. I find that for trivial examples the copy is optimized away, but that on many compilers at various levels of call depth the copy construction occurs causing a huge performance degradation. I suspect that the 'right way' is still by using references in C++03 and by using move constructors in C++0x.
What I'm doing in this code seems reasonable - should it be supported by const ref overloads, or have I missed some 'gotcha' somewhere?
You are not missing anything at all. The const overload should be there and will always be there in Boost.Range.
Thanks,
- Rob.
Sorry for any confusion and wasted time, Neil Groves