关于 c ：传递函数作为参数以使用 lambda 集成对象

double calculus::integralSimple(std::function<double(double)> fn, double begin, double end)
{
    double integral = 0;
    for (long double i = begin; i < end; i += _step)
    {
        integral += fn(i) * _step;  // _step defined in class
    }
    return integral;
}

calculus cl;
std::cout << cl.integralSimple(calculus::identity,0,1);
std::cout << cl.integralSimple([](double x) { return x*x; }, 0, 1);

std::cout << cl.integralSimple( x*x ,0,1); // Always take a function of this form
std::cout << cl.integralSimple( x*sin(x) – x*x ,0,1);

#include <iostream>
#include <vector>
#include
#include <cmath>
#include <boost/lambda/lambda.hpp>
#include <boost/lambda/bind.hpp>

const double PI  =3.141592653589793238463;

double func(double v) { return std::sin(v); } // to avoid having to
                                              // cast std::sin

int main()
{
    using namespace boost::lambda;

    std::vector<double> v = {0, PI / 4, PI / 2, PI};

    std::for_each(v.begin(), v.end(),
        std::cout << _1 * bind(func, _1) – _1 * _1 << ‘/
‘
    //                    a?‘a?‘a?‘a?‘a?‘a?‘a?‘a?‘a?‘a?‘a?‘a?‘a?‘a?‘
    //                    to delay invocation of func
    );
}

auto x = _1;

auto sin(decltype(_1) ) {
    return bind(static_cast<double(*)(double)>(std::sin), _1);
}

std::for_each(v.begin(), v.end(),
    std::cout << x * sin(x) – x * x << ‘/
‘);