Why C++ lambda is slower than ordinary function when called multiple times?

Question

I just have tried to compare performance of lambda expressions in C++11, so I did the test -- compute sum of elements in a vector of double values. Here is the

Answer 1

It turned out, that this is not any issue with lambda expressions, just the compiler optimized-out the outer loop in the first case by caching the result of the sum() function. After change the first case to this form:

out = 0.0;
for (size_t i = 0; i < MAX; ++i)
{
    out += sum(v);
    v[i] = 1.0; // this adds O(1) time and prevents caching
}

both cases timings are approximately equal, with lambda as a favourite.