Calling a std::function is generally a bit slower than executing a lambda as a little more code is involved, for example, executing 1 million function calls for a std::vector of the explicit lambda type versus a std::vector of a corresponding std::function as follows.
Benchmark invocation without capture of lambda vs std::function:
| Lambda | std::function |
auto test_direct_lambda() { auto lbd = [](int v) { return v * 3; }; using L = decltype(lbd); auto fs = std::vector<L>{}; fs.resize(1’000’000, lbd); auto res = int{0}; for (const auto& f: fs) { res = f(res); } return res;} |
auto test_std_function() { auto lbd = [](int v) { return v * 3; }; using F = std::function<int(int)>; ... |
