Project #4: Fractional Wrapper

Objectives

• 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, 1e18], 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.

• This Fractional Wrapper can conform to the ERC4626 specification.

Process

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

Contracts

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*).