Fractional Wrapper

yieldprotocol/mentorship2022#4

Objectives

1. Users can send a pre-specified ERC-20 token (underlying) to another contract that is also an ERC-20, called Fractional Wrapper.
2. The Fractional Wrapper contract issues a number of Wrapper tokens to the sender equal to the deposit multiplied by a fractional number, called exchange rate, set by the contract owner. This number is in the range of [0, 1000000000000000000], and available in increments of 10**-27.
3. 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.

Functions

constructor()

• set the exchange rate
• instantiates underlying ERC-20 token contract address

deposit()

• receives underlying ERC-20 token from user
• calculates corresponding number of wrapper tokens using the exchange rate, and rebase to 1e27
• mints wrapper tokens to the user
• emits a Deposit event

withdraw()

• receives wrapper tokens from user
• calculates corresponding number of underlying tokens, and rebase to 1e18
• transfers underlying tokens to user
• emits a Withdraw event

convertToShares()

• converts an underlying token (asset) to its equivalent amount in shares
• returns uint256

convertToAssets()

• converts shares to its equivalent amount in underlying tokens (asset)
• returns uint256

References

https://eips.ethereum.org/EIPS/eip-4626 https://github.com/yieldprotocol/yield-utils-v2/tree/main/contracts/math