That widget argument should really be const Widget&. Then my statement above stands. I was going under the assumption that the entire response is some function of the input, and the input outlives everything else.

> I'm not entirely sure what the purpose of the transformed_data vector is.

I suppose that in the real application, they want something like 'response = f(g(h(...(input)...))', where f . g . h is some non-trivial composition of a bunch of view transforms. So then it kinda makes sense. Basically, construct a lazy list, then eval everything at the end and store the result somewhere.

If so, then that 'f . g . h' composition might compile to something faster than the equivalent of 3 loops and vectors for intermediate results, since the compiler can fuse the whole thing into a tight loop. They might have made the benchmark misleading by constructing a too-minimal example.