Users can send a pre-specified erc-20 token (underlying) to an ERC20 contract(Fractional Wrapper).

Fractional Wrapper contract issues a number of Wrapper tokens to the sender, equal to the deposit multiplied by a fractional number, called exchange rate. Exchange rate is set by the contract owner.

This number is in the range of [0, 1000000000000000000], and available in increments of 10**-27. (ray).

At any point, a holder of Wrapper tokens can burn them to recover an amount of underlying equal to the amount of Wrapper tokens burned, divided by the exchange rate.

1. User sends DAI to FWrapper.
2. User receives wDAI(wDAI = DAI * ex_rate)
3. Exchange rate set by FWrapper owner
4. Ex_rate is has decimal precision of 10**27 precision
5. User can liquidate and get back underlying DAI, (wDAI is burnt) ---> dai_qty = wDAI/ex_rate

1. DAIToken - underlying
2. FractionalWrapper - "vault w/ ex_rate"
3. Ownable.sol - for onlyOwner modifier, applied on setExchangeRate

Both contracts are ERC20Mock, to issue tokens. FractionalWrapper must conform to ERC4626 specification.

• all methods must be implemented
• implementation of convert* and preview* will be identical in this case (no need to calculate some time-weighted average for convert*).

maxDeposit/maxMint

• dropped receiver param as specified in EIP4626, as there was no need for it in this use case.
• made virutal so it can be overwritten for another use case.