A way to remove duplicated code for & and &mut?

[alice]

See also this similar thread.

@Liii

The Nomicon strongly asserts that transmuting & to &mut always have undefined behaviour, which might by applicable also to this code. But I think Nomicon is talking about code which simultaniously keeps and uses shared and multible references. This code doesn't do that.

It is always UB to cast &T to &mut T under all circumstances. Even if the & originated from a &mut, the compiler added extra assertions on the pointer after it was made immutable that you can't just ignore.