ERC777SnapshotWrapper

ERC777SnapshotWrapper is an ERC777 compliant token contract that serves as a wrapper of an arbitrary ERC20 token. This means that the wrapped token can only be minted / burnt by depositing or withdrawing the underlying ERC20 tokens.

Methods

Beside the standard methods as defined in EIP777 the following additional methods have been implemented to support wrapping and snapshots.

Constructor

• Parameters: address _backingToken; string _name, string _symbol, address[] _defaultOperators
  • _backingToken: the address of the ERC20 token contract that is to be wrapped.
  • _name: name to be used for the wrapping token
  • _symbol: symbol to be used for the wrapping token (for example: DAI, USDT, WETH)
  • _defaultOperators: list of default operators as defined in EIP777

Minting / Reedeming

• depositFor(address, uint256)

  Pulls the backing ERC20 token and mints wrapper tokens 1:1. Requires the msg.sender to have approved the wrapper token contract prior to calling.

  • Parameters: address _recipient; uint256 _amount
    • _recipient: the address to receive the newly minted wrapper tokens
    • _amount: the amount of backing tokens to deposit, consequently also represents the exact amount of wrapper tokens to be minted
  • Events: This method emits no special events beside the events defined in the EIP777 standard (Minted, Transfer)

• mintTo(address, uint256)

  Uses excess backing token balance to mint tokens (balance - totalSupply). Useful for contracts wishing to mint wrapper tokens as no approval is necessary. Contracts can atomically send the backing tokens to the wrapper contract and subsequently use mintTo to mint the wrapped equivalent.

  • Parameters: address _recipient; uint256 _amount
    • _recipient: the address to receive the newly minted wrapper tokens
    • _amount: amount of wrapper tokens to mint. Reverts if _amount is above the available excess
  • Events: This method emits no special events beside the events defined in the EIP777 standard (Minted, Transfer)

• withdrawTo(address, uint256)

  Redeems wrapper tokens for underlying backing token by burning wrapper tokens from the msg.sender.

  • Parameters: address _recipient, uint256 _amount
    • _recipient: recipient of redeemed backing tokens
    • _amount: amount to burn and subsequently release
  • Events: This method emits no special events beside the events defined in the EIP777 standard (Burned, Transfer)

Snapshots

• snapshot() -> (uint256)

  Creates a new snapshot returning the new snapshotId

  • Return value(s):
    • uint256 snapshotId: ID of newly created snapshot. Can be used to retrieve balances and totalSupply as they were at the time of the creation of the snapshot
  • Events:
    • Snapshot(uint256 snapshotId):
      • uint256 snapshotId: ID of new snapshot

• [view] balanceOfAt(address, uint256) -> (uint256)

  Retrieves historical balance. Will return the balance of the address as it was when the snapshot was created.

  • Parameters: address _account; uint256 _snapshotId
    • _account: address of account for which to retrieve the historical balance
    • _snapshotId: the ID of the snapshot to reference
  • Return value(s):
    • uint256 balance: historical balance of wrapper token for the querried account

• [view] totalSupplyAt(uint256) -> (uint256)

  Similar to balanceOfAt retrieves the historical totalSupply at different snapshots.

  • Parameters: uint256 _snapshotId
    • _snapshotId: the ID of the snapshot to reference
  • Return value(s):
    • uint256 totalSupply: historical totalSupply of the wrapper token at snapshot