See also #5 and #11
Returning a borrowed reference is fundamentally unsafe.
There are conditions where it can be done safely, but each case requires careful analysis, and is often, if not usually, the case that the analysis is done incorrectly.
For example, #5 (comment) suggests that it is fine to return a borrowed reference to a tuple element.
However, it is only safe if a reference to the tuple is held on the stack. If the only reference to the tuple is on the heap, then borrowing a reference to an element of the tuple is unsafe, as mutation of a heap object could result in the reference to the tuple, and its element vanishing.
I think it is better to say that returning a borrowed reference is always unsafe, than rely on flawed assumptions about performance and faulty reasoning about lifetimes.
See also #5 and #11
Returning a borrowed reference is fundamentally unsafe.
There are conditions where it can be done safely, but each case requires careful analysis, and is often, if not usually, the case that the analysis is done incorrectly.
For example, #5 (comment) suggests that it is fine to return a borrowed reference to a tuple element.
However, it is only safe if a reference to the tuple is held on the stack. If the only reference to the tuple is on the heap, then borrowing a reference to an element of the tuple is unsafe, as mutation of a heap object could result in the reference to the tuple, and its element vanishing.
I think it is better to say that returning a borrowed reference is always unsafe, than rely on flawed assumptions about performance and faulty reasoning about lifetimes.