Re: [Boost-users] Making an ordinary function into something useful in lambda expressions

On 12/10/2007, Peter Waller wrote:

I wish to write some lambda functions to have this sort of behaviour.

#include #include #include

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 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 fn = bind(static_cast(&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