Take a `unique_ptr<widget>&` parameter to express that a function reseats the `widget`

Reason

Using unique_ptr in this way both documents and enforces the function call's reseating semantics.

Note

"reseat" means "making a pointer or a smart pointer refer to a different object."

Example

void reseat(unique_ptr<widget>&); // "will" or "might" reseat pointer

Enforcement

• (Simple) Warn if a function takes a Unique_pointer<T> parameter by lvalue reference and does not either assign to it or call reset() on it on at least one code path. Suggest taking a T* or T& instead.