lambda as default parameter

#include <iostream>
#include <functional>

template<typename T>
struct dimension {
    T v_;
};

template<typename T, typename F = std::function<T(T)>>
T drawfield(dimension<T> src, F func = [](T v){return v;}) {
    return func(src.v_);
}

int main() {
    const auto a = drawfield(dimension<int>{3});
    std::cout << "a: " << a << std::endl;

    const auto b = drawfield(dimension<int>{4}, [](int v) { return v*2; });
    std::cout << "b: " << b << std::endl;
}