Optimizing memory usage

The method we've discussed so far, for structuring code in a functional way, involves passing multiple times through a collection that is treated as immutable. As a result, this can lead to copies of the collection. Let's look, for example, at a simple code sample that uses transform to increment all the elements of a vector:

template<typename DestinationType>
auto transformAll = [](const auto source, auto lambda){
    DestinationType result;
    transform(source.begin(), source.end(), back_inserter(result), 
        lambda);
    return result;
};

TEST_CASE("Memory"){
    vector<long long> manyNumbers(size);
    fill_n(manyNumbers.begin(), size, 1000L);

    auto result = transformAll<vector<long long>>(manyNumbers, 
        increment);

    CHECK_EQ(result[0], 1001);
}

This implementation leads to a lot of memory allocations...