Function singleton_cell::with_token

pub fn with_token<R>(f: impl for<'brand> FnOnce(Token<'brand>) -> R) -> R

Generate a local token type which is guaranteed to be a singleton via a unique lifetime brand. SCells can be created within this scope via SCell::new or SCell::from_mut and used via this token.

This token and all borrows and cells based off of it cannot escape the scope.

 use singleton_cell::*;

 let mut x = 0;
 with_token(|mut tok| {
     let cell_borrow = &*SCell::from_mut(&mut x);
     *cell_borrow.borrow_mut(&mut tok) += 2;

     let cell_one = SCell::new(0);
     *cell_one.borrow_mut(&mut tok) += 1;
     cell_one.into_inner()
 });
 assert_eq!(2, x);