Transform into a const vector

Question

I have some vector of Foos at hand and I want to transform it into a vector of Bars, and a const one. The best way I can think of is:

Bar foo2bar(const Foo& foo);

std::vector<Foo> foos = {...};

const std::vector<Bar> bars = [&foos] {
    std::vector<Bar> bars;
    bars.reserve(foos.size());
    std::transform(foos.cbegin(), foos.cend(),
                   std::back_inserter(bars),
                   foo2bar);
    return bars;
}();

And I think the return value of the lambda should be elided by most compilers, so this should be close to ideal. The only disadvantage is probably the need to create a lambda, but I don't think it's too much of a problem.

Is there any insidious problem with this approach, and is there any better way (e.g., faster, cleaner)? C++11 is available.

Answer 1

Your simplest solution is to drop the const requirement altogether. You can still expose a reference-to-const to other scopes.

Failing that, this should be fine. The lambda body will probably be inlined, "creation" of the lambda is a compile-time process, and the return value will either be moved or elided altogether. Your approach is quite elegant, actually.