CppCoreGuidelines T.40 通过函数对象传递操作符给算法

bool greater(double x, double y) { return x > y; }
// pointer to function: potentially slow
sort(v, greater);
// function object
sort(v, [](double x, double y) { return x > y; });
// function object
sort(v, std::greater{});

bool greater_than_7(double x) { return x > 7; }
// pointer to function: inflexible
auto x = find_if(v, greater_than_7);
// function object: carries the needed data
auto y = find_if(v, [](double x) { return x > 7; });
// function object: carries the needed data
auto z = find_if(v, Greater_than<double>(7));

// require an ordered type
auto y1 = find_if(v, [](totally_ordered auto x) { return x > 7; });
// hope that the type has a >
auto z1 = find_if(v, [](auto x) { return x > 7; });