Membership and the address list

Most governance plugins need a notion of "who counts": multisig signers, addresslist voters, token holders. Two reusable pieces standardize that.

IMembership: the discovery interface

Any plugin that defines membership should implement IMembership, a tiny interface, isMember(address) plus MembersAdded / MembersRemoved events. Its real value is discoverability: UIs and indexers can query and track membership uniformly across every plugin.

It also allows delegated membership via MembershipContractAnnounced: a plugin can point at a different contract as the authority on membership (e.g. an external token) instead of maintaining a list itself. That's how a token-voting plugin says "membership = holders of this token", the token is the membership source, and the event tells indexers where to look.

Addresslist: a snapshot-safe member list

When a plugin does maintain its own member set (multisig, addresslist voting), Addresslist is the building block. Its defining feature is that it's checkpointed: membership and the total member count are recorded per block, so you can ask "was this address a member at block N?" and "how many members were there at block N?".

Why that matters: governance must compute eligibility and thresholds against the state as of a proposal's snapshot block, not the current block. Otherwise someone could join right before voting, or the member count could shift mid-vote, opening the door to flash-membership manipulation. Checkpointing (the same technique OpenZeppelin's ERC20Votes uses) makes those queries historical and therefore tamper-resistant.

isListed(account)                       // member right now
isListedAtBlock(account, blockNumber)   // member as of a past block (snapshot)
addresslistLength()                     // current member count
addresslistLengthAtBlock(blockNumber)   // count as of a past block

_addAddresses / _removeAddresses maintain the list (rejecting double-adds and removing non-members). Combined with Ratio for threshold math, this is the backbone of the addresslist-based voting and multisig plugins.

Keep in mind

• Decide against the snapshot block, not "now". Query membership and counts with the …AtBlock variants at a proposal's snapshot; using current state lets membership changes mid-vote distort eligibility or thresholds.

See also

• Ratio — turning a member count into a required threshold.
• Proposals — the other half of a governance plugin.
• The plugins area — where these are put to use.