Not so much of an error with the site itself, more of an issue with the content. On the left, it's explaining how if you assign a unique_ptr to another unique_ptr, it will assign the pointer and then the original will not be usable. What ACTUALLY happens if you try this is the file won't even compile because that's an illegal assignment. This is the first time I've seen something explicitly described as being possible when in reality it's not. I'm somewhat new to C++, so I could be wrong, but all the sources I've found say that's not a thing you can do, and even the program itself won't compile within the simulated desktop.
You’re correct that mc2 = mc; won’t compile. The copy assignment operator for unique_ptr is explicitly deleted, which is what the compiler error in your screenshot is reporting. A unique_ptr can’t be copied at all.
The behavior the notebook is describing — assigning one unique_ptr to another and having ownership transfer over — is actually how move works, not copy. And it requires an explicit std::move:
mc2 = std::move(mc);
The whole point of unique_ptr is that this transfer can’t happen silently — you have to opt in with std::move.
So this is a genuine mistake in the lesson content, and we’ll get the passage corrected right away. Thanks for flagging it clearly.
