module 0x42::example {
  struct Coin<T> {
    amount: u64
  }
  struct Receipt<phantom T> {
    amount: u64
  }
 
  public fun flash_loan<T>(_user: &signer, amount:u64): (Coin<T>, Receipt<T>) {
    let (coin, fee) = withdraw(user, amount);
    (coin,Receipt { amount: amount + fee})
  }
 
  public fun repay_flash_loan<T>(rec: Receipt<T>, coins: Coin<T>) {
    let Receipt{ amount } = rec;
    assert!(coin::value<T>(&coin) >= rec.amount, 0);
    deposit(coin);
  }
}