Re: [Boost-users] [Bind] Understanding protect

On 03/27/2012 10:17 PM, Robert Jones wrote:

On Tue, Mar 27, 2012 at 7:25 PM, Gordon Woodhull mailto:gordon@woodhull.com> wrote:

On Mar 27, 2012, at 2:13 PM, Robert Jones wrote: > Ultimately I'm doing this for each member of a > range, via std algorithm, so I need to bind a unary argument to produce a nullary function > object, which I can then pass to an evaluation context, ie my g( ) function. If I've generated > the function object with bind and placeholder(s), it seems there's no way to prevent the binding > of the last placeholder from triggering evaluation, when what I require is an unevaluated nullary > function object.

Hmm, works for me, IIUC:

#include #include <iostream>

template<typename F> void g(F const &f) { f(); }

void f(int x) { std::cout << "x is " << x << std::endl; }

int main() { for(int i=0; i<7; ++i) g(boost::bind(f,i)); return 0; }

But how would that translate to this context...?

int main( ) { std::vector<int> v; v += 0,1,2,3,4,5,6; for_each( v.begin( ), v.end( ), /* ???? */ ); return 0; }

Thx, Rob.

You might also want to consider phoenix::lambda, it is like protect, but slightly more powerful. your example would then read: #include int main( ) { std::vector<int> v; v += 0,1,2,3,4,5,6; using boost::phoenix::bind; using boost::phoenix::lambda; using boost::phoenix::placeholders::_1; using boost::phoenix::local_names::_1; for_each( v.begin( ), v.end( ), bind(g, lambda(_a = _1)[bind(f, _a)])); return 0; }