Release Candidate for Contracts 4.2

General Announcements
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This release contains the first part of our work on governance contracts. The new ERC20Votes and ERC20VotesComp extensions to the ERC20 token include vote delegation mechanisms essential to using these tokens for voting in governance systems like Compound’s GovernorAlpha and GovernorBravo.

The full changelog is listed below. Try it out and provide any feedback before the final release one week from now!

Changelog

  • ERC20Votes: add a new extension of the ERC20 token with support for voting snapshots and delegation. (#2632)
  • ERC20VotesComp: Variant of ERC20Votes that is compatible with Compound’s Comp token interface but restricts supply to uint96. (#2706)
  • ERC20Wrapper: add a new extension of the ERC20 token which wraps an underlying token. Deposit and withdraw guarantee that the total supply is backed by a corresponding amount of underlying token. (#2633)
  • Enumerables: Improve gas cost of removal in EnumerableSet and EnumerableMap.
  • Enumerables: Improve gas cost of lookup in EnumerableSet and EnumerableMap.
  • Counter: add a reset method. (#2678)
  • Tokens: Wrap definitely safe subtractions in unchecked blocks.
  • Math: Add a ceilDiv method for performing ceiling division.
  • ERC1155Supply: add a new ERC1155 extension that keeps track of the totalSupply of each tokenId. (#2593)
  • BitMaps: add a new BitMaps library that provides a storage efficient datastructure for uint256 to bool mapping with contiguous keys. (#2710)

Breaking Changes

  • ERC20FlashMint is no longer a Draft ERC. (#2673))
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