Because of the name, the finalize helper might easily be misunderstood as "finishing" a document being constructed, whereas it actually destructively steals the constructed document and returns it, leaving the builder with empty state.

Consider the following example:

using bsoncxx::builder::stream::document;
using bsoncxx::builder::stream::finalize;

document one;
one << "key" << "value";
std::cout << bsoncxx::to_json(one.view()) << std::endl;

document two;
two << "key" << "value" << finalize;
std::cout << bsoncxx::to_json(two.view()) << std::endl;

The result is:

{
    "key" : "value"
}
{

}

If we rename finalize to something more self-documenting (and alarming) like steal_document, the API would be harder to mistakenly misuse.

For example:

document two;
two << "key" << "value" << steal_document;

That is obviously a mistake. It also makes clear what assignment is doing:

document three;
auto doc = three << "key" << "value" << steal_document;