comment on ep205 lambda as a way to take benefit of (N)RVO

[Dharmesh946]

Sorry I didn't find the ep205 corresponding "issue".

In this episode and in some previous one on lambda. It is claimed that lambdas can be used to optimize some variable creation. The canonical example given is

#include <vector>

void f() {
    const auto value = []() {
        std::vector<int> vec(10, 10);
        vec.push_back(42);
        return vec;
    }();
}

Yet

#include <vector>

void g() {
    std::vector<int> vec(10, 10);
    vec.push_back(42);
    const auto value = std::move(vec);
}

seems to lead to the exact same assembly : https://godbolt.org/z/bc6TxY7vW. This more verbose snippet, shows also that NRVO might fail inside the lambda (which are submitted to the same rules as regular functions) : https://godbolt.org/z/hG1qT18K1

Would it be possible to have a clarification?

[Dharmesh946]

from https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Res-lambda-init I guess that it comes useful in case of not movable intermediate object?