[Boost-users] Re: composition and arguement binding: what touse:boost::bind vsboost::mpl vs boost::lambda

Peter Dimov wrote:

Kevin Wheatley wrote:

...

Subsequently, the containers now contain std::pair's to shared_ptrs, so I have even more composition going on, which for a one off 'function' is getting messy, with Lambda it should be much simpler so I'd certainly like to know if I missed something with this.

Extracting a member of a pair is equally painful with Bind and Lambda: bind(&Pair::second, _1). Lambda also supports _1->*&Pair::second for ordinary pointers, but not for shared_ptr, where you'll need something like &*_1->*&Pair::second.

Peter, Thanks for the reply. It's all starting to look rather like Perl at this point and as such my inbuild parser is failing to parse what that does at a glance (can't work out what set of rules I've got to use :-), so it might be worth avoiding just so that mortals can simply see what is going on! I guess if Lambda understood about smart pointers in a similar way to Bind some of this syntax could be simplfied. see attatched for what I'd like to do. Kevin -- | Kevin Wheatley, Cinesite (Europe) Ltd | Nobody thinks this | | Senior Technology | My employer for certain | | And Network Systems Architect | Not even myself | #include <vector> #include <algorithm> #include <iostream> #include <cstddef> #include #include #include // So don't do this in real code it is not stylish using boost::shared_ptr; using namespace boost::lambda; using namespace std; int main(int /*argc*/, char** /*argv*/) { const int numberValues = 10; vector<int> vi(numberValues); for_each(vi.begin(), vi.end(), _1 = 1); // Assign the value 1 to all vi[numberValues / 2] = -1; vector vpi(numberValues); transform(vi.begin(), vi.end(), vpi.begin(), &_1); // Assign the addresses to the pointers for_each(vpi.begin(), vpi.end(), cout << _1 << constant(' ') << *_1 << constant('\n')); vector vspi(numberValues); for (size_t i = 0; i != vspi.size(); ++i) // Fill with a sequence of new integers [0..numberValues] vspi[i].reset(new int(i)); // N.B. Can't use boost::lambda::bind with operator new() // Ignore the unsigned mismatch warning. for_each(vspi.begin(), vspi.end(), cout << bind(&shared_ptr<int>::get, _1) << constant(' ') << *bind(&shared_ptr<int>::get, _1) << constant('\n')); for_each(vspi.begin(), vspi.end(), cout << _1 << constant(' ') << *_1 << constant('\n')); // Fails here return 0; }