Macro rfc_borrow

macro_rules! rfc_borrow {
    ($this:ident, $func:expr) => { ... };
    ($this:ident, $rfc_field:ident, $func:expr) => { ... };
}

Intended to be used with a std::cell:RefCell that is a field of $this.

Calls “borrow” on the RefCell field and passes the result and a reference to $this to the provided $func expression.

If no $rfc_field is provided (first case) then the name “mut_state” is used for the $rfc_field.