Function echo 

pub fn echo(cell: &RefCell<u128>) -> impl FnMut(&State) -> u128 + '_

A pre-canned delegate that parrots the value in the given cell.

Examples

use std::cell::RefCell;
use tinyrand::{Rand, RefCellExt};
use tinyrand_alloc::{Mock, echo};

let cell = RefCell::default();
let mut mock = Mock::default().with_next_u128(echo(&cell));
assert_eq!(0, mock.next_u64());
cell.set(42);
assert_eq!(42, mock.next_u64());