Instead of storing a pointer to the QJsonArray or QJsonObject (like the Qt 4 & pre-5.15 versions did), do like QCborValueConstRef and store the pointer to the QCborContainerPrivate. Unlike QCborValueRef, we must keep the is_object bit because of API behavior that assigning an Undefined to an object reference deletes it from the container. I've chosen to use size_t instead of qsizetype for this because then we don't lose any bits of the index. Therefore, the index in the case of objects is stored as pair count (like before), different from QCborValueRef which stores the actual index in the QCborContainerPrivate. It's the LSB (on little-endian architectures) so the calculation of 2 * index + 1 is the actual value stored in memory or in the register. Unfortunately, right now, both Clang and GCC don't realize this and generate unnecessary instructions. Clang: 0000000000000000 <QJsonValueConstRef::concreteType(QJsonValueConstRef)>: 0: mov %rsi,%rax 3: shr %rax 6: mov %rsi,%rcx 9: or $0x1,%rcx d: test $0x1,%sil 11: cmove %rax,%rcx [GCC code is identical, except it uses an AND instead of TEST] That OR at offset 9 is a no-op because it sets a bit that is already set in those conditions. At least they don't do unnecessary shifts. Change-Id: I89446ea06b5742efb194fffd16bb7aadb6a9b341 Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>