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Niels Lohmann
0c0d5edda3
insert(const_iterator pos, basic_json&& val) delegated to insert(pos, val), but val is a named rvalue reference, so inside the function it is an lvalue: the call always resolved to insert(const_iterator, const basic_json&) and deep-copied the value. This has been the case since the overload was introduced, in every release. push_back(basic_json&&), by contrast, already moves. Give the rvalue overload its own body with the same two checks (type_error.309, invalid_iterator.202), then move the argument into a local before inserting it. Moving into a local first, rather than inserting std::move(val) directly, keeps this safe even when val aliases an element of the same array (e.g. arr.insert(arr.begin(), std::move(arr[1]))), since std::vector::insert(pos, T&&) is not guaranteed to handle an argument that aliases one of its own elements. This is a deliberate, small behavior change: the moved-from argument now ends up null afterwards, the same as after push_back(&&), instead of keeping its old value unchanged. No signature changes, so the public API and ABI are unaffected. Add unit-modifiers coverage for the moved-from state and for self-aliasing insertion, both with and without reallocation of the underlying array. Part of #5724 Signed-off-by: Niels Lohmann <mail@nlohmann.me>