On 12/10/2007, Peter Waller <peter.waller@gmail.com> wrote:
I wish to write some lambda functions to have this sort of behaviour.
#include <lambda/lambda.hpp> #include <lambda/bind.hpp> #include <function.hpp>
using namespace boost::lambda; using namespace boost;
#include <iostream> using std::cout; using std::endl;
#include <cmath>
int main( int argc, char *argv[] ) { float value; var_type<float>::type theValue( var( value ) );
// Ignore this line #define cos(theta) bind( unlambda(bind( cos, _1 )), theta )
function<float ( float )> myfunction = ( cos( theValue ) - 1 ); value = 2; cout << "The result = " << myfunction(1) << endl; return 0; }
Namely, the cos( value ) part.
The code above works, but I feel that using a #define is a little messy, and seems hard to generalise to functions with more arguments. I was wondering if there was a general, better way of turning a given function into one whose execution is delayed.
Thanks in advance,
- Peter
This seems to work: double value = 3.14159 / 2.0; boost::function<float(void)> fn = bind(static_cast<double(*)(double)>(&cos), var(value)); std::cout << fn() << std::endl; value = 0.0; std::cout << fn() << std::endl; At least, the output of 'fn()' changes when 'value' changes, which (as far as I could tell) was what you wanted? The static_cast is needed to select the appropriate 'cos' overload. HTH Stuart Dootson